Over two eight‐month periods (October/November‐May) during successive winters (1983/4 and 1984/5), the body temperatures and activity patterns of captive badgers, Meles meles, living under semi‐natural conditions, were studied at 57 d̀N in Scotland. Temperature‐sensitive radio transmitters and automated telemetry systems provided long‐term records of body temperatures and times badgers were absent from an artificial sett.Badger body temperatures of 28–34 d̀C, significantly below euthermic levels, were recorded between October/November and March each winter, with differences between mean daily maxima and minima varying from 1.6 to 8.9 d̀C. This was associated with a reduction, by up to 90%, in the time that the badgers spent outside their sett in mid‐winter. Body temperatures did not show circadian cyclicity, but from February onwards most locomotor activity occurred between 22:00 and 02:00 GMT. The extent to which activity was concentrated around midnight increased with decreasing night length in spring.The body temperatures of one female badger fell to a nadir of 28 d̀C immediately prior to ovo‐implantation. During post‐implantation gestation, the body temperature of this female rose steadily, but had reached only 34.6 d̀C at parturition.Photoperiod correlated closely with seasonal changes in body temperatures and activity levels, and is suggested as the primary synchronizer of seasonal activity and body temperature cycles. Other environmental variables, particularly ambient temperature and snow‐cover, appeared to act as modulating influences on these cycles.It is postulated that during the winter, when climatic conditions are responsible for a shortage of food and an increase in heat loss, winter lethargy is an adaptation which enables the European badger to maintain energy balance. Reduced activity and confinement within sheltered setts, together with reduced body temperatures, enable the badgers to rely heavily on energy stored in adipose tissue during the autumn.