Abstract The size‐frequency distribution, sex ratio, and visceral index in a population of the aspidochirote holothurian Stichopus mollis (Hutton, 1872) were studied on the north‐east coast of New Zealand. Adult Stichopus mollis ranged in length from 13 to 25 cm, and showed a unimodal size‐frequency distribution. Young S. mollis were rare, and were found under boulders in the shallow subtidal zone (5–8 m). The population of S. mollis under study showed a 1 : 1 sex ratio; three hermaphrodites were found. The viscera index maintained an approximately uniform value throughout the reproductive season. No evidence was found for spontaneous evisceration or seasonal atrophy of the viscera. Two predatory attacks on S. mollis by the asteroid Luidia varia were observed.