The movie was shot entirely in Ottawa, Canada so for the jungle scenes that appear at the beginning and end of the movie, palm trees were brought in to make the location look tropical.
Trevor Matthews, who plays Jack Brooks, also plays the troll that kills his family. At the end it is not Trevor's hand or boot on the dying troll, it is special effects makeup artist David Scott's.
Trevor Matthews and Jon Knautz thought of the idea for 'Jack' while making up horror stories at Trevor's cottage in the 1000 Islands near Kingston, Ontario.
The sign on the desk of Dr. Silverstein, Jack Brooks' shrink, misspells "counselor" as "councilor". (Despite various international spellings, a "councilor" is still someone who works for the council, and a "counselor" is someone who counsels.)