The aim of this postal survey was to highlight differences in temperament and behaviour between 32 toddlers in Japanese families living temporarily in London and 36 in British families, all in London. Mothers completed questionnaires about demography, perinatal events, and their child's temperament and behaviour. UK toddlers were described as exhibiting fewer behavioural symptoms than Japanese toddlers. Significantly more of the Japanese toddlers scored above the cutoff on the Behaviour Check List, indicating higher levels of behavioural disturbance. An interesting item is ‘sleeping with parent’, which occurs commonly in Japanese families and is considered to be normal for that culture. On the Toddler Temperament Scale the Japanese toddlers proved more distractable and more intense than the UK toddlers when age had been allowed for. It was of interest that Japanese girls proved more distractable than Japanese boys and UK girls. Possible explanations for the differences are advanced.