Summary. The aetiology of sudden infant death syndrome (SIDS) is still uncertain, although associations with overheating and the prone sleeping position have been reported. In the UK, the incidence of SIDS is considerably lower in infants of Asian origin, but as yet no explanation for this has been suggested. We have studied a group of 202 white and 172 Asian multiparous mothers attending an antenatal clinic to compare the sleeping position and home environment of infants in each ethnic group. We found that significantly more white infants (31%) than Asians (11%) were placed in the prone position at night and that 94% of Asian infants slept in their parents' bedroom, compared with 61% of whites. These observations demonstrate marked differences in the infant rearing practices favoured by Asians and whites and lend support to the concept that the prone position and separate bedrooms may be contributors to the development of sudden infant death.