Brown tree snakes (Boiga irregularis) are medium to large colubrid snakes that are relatively common within the eastern and northern parts of tropical Australia. An invasive population on Guam in the western Pacific has resulted in B. irregularis being one of the most studied snakes on earth. However, no field studies have ever been conducted on Australian populations. During a seven-year period we collected data on 265 field-caught specimens in north Queensland. These snakes were from three populations and provided data on body sizes, activity times, food habits and reproduction. B. irregularis were found to attain larger body sizes in the Wet Tropics populations than in the Townsville and Magnetic Island populations. More snakes were encountered during the wet and warm season than during the dry and cool season. Sexual size dimorphism was not detected in any population. The diet included a wide range of vertebrates. Reproductive data were scant from the populations examined.