<b>Interactivity in Goodsalls Rule and Fistula in ano</b> Fistula in ano is a tract lined by granulation tissue which opens deeply in the anal canal or rectum and superficially on the skin around the anus. Managing fistula in ano is a challenging task. Because recognizing the internal opening and cause of the fistula tract is difficult. Both external and internal openings of the fistula tract are essential for the complete identification of the tract. The purpose of the present study was to study the relevance between Goodsall s rule and course of the fistula tract. A sample of 106 patients with simple fistula was studied. In this study Hydrogen Peroxide was injected by using syringe through the external opening of the fistula and seenthe appearance of air bubbles which are come out from the internal opening. The site and number of internal and external openings and the course of the tract were recorded. The median age of the participants was 37 years. The majority were male 57.54 . Thirty one point one percent 31.1 showed intersphincteric fistula, 51.8 showed transphincteric fistula and 16.9 had superficial fistula. The overall predictive accuracy of Goodsall s rule in studied group was 68.3 . It is significantly associated with the type of fistula. The high predictive accuracy in superficial fistula 94.4 , intersphincteric fistula 84.4 and transphicteric fistula 69.09 were observed. It was concluded that, Goodsalls rule was not accurate in 31.7 of all fistulae it can be used as a guide in locating the course of the tract and the internal opening. Goodsalls rule, fistula in ano, Sri Lankan population 1427-1428 Issue-4 Volume-4 Samaranayake G. V. P | Chandimal K. M