diff --git a/README.md b/README.md
index 823c8a7..8481b70 100644
--- a/README.md
+++ b/README.md
@@ -16,6 +16,15 @@ source file in the right window.
 
 You can configure the following settings:
 
+### g:splitopen_extensions
+
+Use this dictionary to define your pairs of left-hand- right-hand-side file
+types. E.g.
+
+	let g:splitopen_extensions = {"h": "cpp"}
+
+always places a .cpp file on the right-hand side when opening an .h file and
+vice versa.
 
 ### g:splitopen_set_fzf_keys
 
diff --git a/autoload/splitopen.vim b/autoload/splitopen.vim
index 98aa3b0..b4488ba 100644
--- a/autoload/splitopen.vim
+++ b/autoload/splitopen.vim
@@ -1,3 +1,22 @@
+function s:invert_dict(source_dict)
+	let result = {}
+	for [key, value] in items(a:source_dict)
+		let result[value] = key
+	endfor
+	return result
+endfunc
+
+let s:extensions = g:splitopen_extensions
+let s:extensions_rev = s:invert_dict(s:extensions)
+
+function s:isLeftSideExtension(extension)
+	return has_key(s:extensions, a:extension)
+endfunc
+
+function s:isRightSideExtension(extension)
+	return has_key(s:extensions_rev, a:extension)
+endfunc
+
 function s:getFileExtension(filename)
 	return fnamemodify(a:filename, ":e")
 endfunction
@@ -6,23 +25,36 @@ function s:getFileRoot(filename)
 	return fnamemodify(a:filename, ":r")
 endfunc
 
-function s:getSwitchExtension(extension)
-	if (a:extension == "cpp")
-		return "h"
-	elseif (a:extension == "h")
-		return "cpp"
+function s:getSwitchExtension(filename)
+	let extension = s:getFileExtension(a:filename)
+	if s:isLeftSideExtension(extension)
+		return s:extensions[extension]
+	elseif s:isRightSideExtension(extension)
+		return s:extensions_rev[extension]
 	endif
 endfunc
 
 function s:getSwitchFile(filename)
-	return s:getFileRoot(a:filename) . "." . s:getSwitchExtension(s:getFileExtension(a:filename))
+	return s:getFileRoot(a:filename) . "." . s:getSwitchExtension(a:filename)
 endfunc
 
 function s:addLeftSplit(filename)
 	execute("vsplit " . s:getSwitchFile(a:filename))
+	execute("wincmd l")
+endfunc
+
+function s:addRightSplit(filename)
+	execute("vsplit " . s:getSwitchFile(a:filename))
+	execute("wincmd L")
+	execute("wincmd h")
 endfunc
 
 function splitopen#SplitOpenFile(filename)
 	execute("tabedit " . a:filename)
-	call s:addLeftSplit(a:filename)
+	let extension = s:getFileExtension(a:filename)
+	if s:isLeftSideExtension(extension)
+		call s:addRightSplit(a:filename)
+	elseif s:isRightSideExtension(extension)
+		call s:addLeftSplit(a:filename)
+	endif
 endfunction
diff --git a/doc/splitopen.txt b/doc/splitopen.txt
index c4b3e6e..ef3aa40 100644
--- a/doc/splitopen.txt
+++ b/doc/splitopen.txt
@@ -5,7 +5,8 @@ CONTENTS                                                     *SplitOpenContents*
 
 	1. Usage ..............................|SplitOpenUsage|
 	2. Configuration ......................|SlitOpenConfiguraton|
-		2.1 g:splitopen_set_fzf_keys.......|SplitOpenConfiguration_set_fzf_keys|
+		2.1 g:splitopen_extensions.........|SplitOpenConfiguration_extensions|
+		2.2 g:splitopen_set_fzf_keys.......|SplitOpenConfiguration_set_fzf_keys|
 	3. License ............................|SplitOpenLicense|
 	4. Changelog ..........................|SplitOpenChangelog|
 
@@ -26,8 +27,18 @@ source file in the right window.
 You can configure the following settings:
 
 --------------------------------------------------------------------------------
+2.1 g:splitopen_extensions                   *SplitOpenConfiguration_extensions*
 
-2.1 g:splitopen_set_fzf_keys               *SplitOpenConfiguration_set_fzf_keys*
+Use this dictionary to define your pairs of left-hand- right-hand-side file
+types. E.g.
+
+	let g:splitopen_extensions = {"h": "cpp"}
+
+always places a .cpp file on the right-hand side when opening an .h file and
+vice versa.
+
+--------------------------------------------------------------------------------
+2.2 g:splitopen_set_fzf_keys               *SplitOpenConfiguration_set_fzf_keys*
 
 Set this option to 1 
 
diff --git a/plugin/splitopen.vim b/plugin/splitopen.vim
index 91cabdd..7f54b02 100644
--- a/plugin/splitopen.vim
+++ b/plugin/splitopen.vim
@@ -1,5 +1,13 @@
 command -nargs=1 SplitOpen :call splitopen#SplitOpenFile("<args>")
 
+" map left-split / right-split file extensions
+if !exists("g:splitopen_extensions")
+	let g:splitopen_extensions = {
+		\	"h": "cpp",
+		\	"H": "CPP",
+		\	}
+endif
+
 if !exists('g:splitopen_set_fzf_keys')
 	let g:splitopen_set_fzf_keys = 0
 endif
@@ -9,5 +17,6 @@ if g:splitopen_set_fzf_keys
 		\	'ctrl-s': 'SplitOpen',
 		\	'ctrl-t': 'tab split',
 		\ 	'ctrl-x': 'split',
-		\ 	'ctrl-v': 'vsplit' }
+		\ 	'ctrl-v': 'vsplit',
+		\	}
 endif