Holothuria atra is the most common epifaunal holothurian on the reef flat at Heron Island. The gonad maturation cycle of H. atra was followed using gonad index estimations and histological examination. Gonad samples were taken at intervals of 6 to 8 weeks for 18 months. Mature gonads occurred in most samples, and gonad maturity peaked twice; in early winter and in summer. Sex ratio of female to male animals was not significantly different from a 1:2 ratio. Sex ratio ranged from 1:8.5 in animals weighing less than 100 g, to 1:0.7 in those over 1,000 g. H. atra commonly reproduces asexually by transverse binary fission. In 21 samples, each of approximately 50 animals, 6% to 70% of individuals were detectable products of asexual reproduction. Occurrence of frequent asexual reproduction compounds difficulties in estimation of growth parameters from data such as size-frequency distributions and growth increments.