$re = '/(?<=#{1,6} (.*)\n(?:(?!#).*\n)*)(?=[+*-] (.*(?:\n(?![#+*-]).*)?))/';
$str = '# Test
## First List
* Hello World
* Lorem
* foo
## Second List
- item
## Third List
+ item 1
part of item 1
+ item 2
## Not a List
bla bla bla
## Empty
## Another List
bla bla bla
bla
* ITEM
## Nested List
### Inside Nested
* foo
* bar';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php