Miniature radio transmitters were surgically implanted in 15 adult diamond pythons from two areas near Sydney, N.S.W., in south-eastern Australia, and the snakes monitored for intervals of 4-32 months. We document patterns of habitat use and movements, and interpret these in terms of the feeding habits and reproductive biology of the pythons. These snakes were usually sedentary in summer and autumn, with occasional long movements to new sites. During spring (the mating season), males moved long distances, often daily. Telemetered pythons were generally diurnal and terrestrial rather than arboreal. Snakes were most commonly recorded coiled under vegetation which provided filtering cover (34% of locations). The relative use of different habitats by diamond pythons changed with season. In summer and autumn, snakes were most frequently in disturbed habitats (such as areas around houses), where prey are relatively common. In winter the snakes used rocky habitats, especially sandstone crevices. No winter aggregations were observed. The radio-tracked snakes had large (up to 124 ha), well-defined but overlapping home ranges, and these varied significantly between sexes and among seasons. Detailed analysis of python movements shows that at least two assumptions of many home-range analyses (normally distributed data and adequacy of small sample sizes) are invalid for our study.