In a rural area of western Kenya, primary schoolchildren's health seeking behaviour in response to common illnesses was investigated. 57 primary schoolchildren (age 11-17 years, median 13 years) were interviewed weekly about their health status and health seeking activities for 30 weeks. The children each experienced on average 25 illness episodes during this period. Most episodes could be categorised into 4 groups: 'cold', 'headache', 'abdominal complaints' and 'injuries'. One fifth (21%) of the illness episodes were serious enough to keep the children from school. In 28% of them, an adult was consulted, while 72% were not reported to an adult caretaker. Of the episodes without adult involvement, 81% remained untreated, while 19% were treated by the children themselves with either herbal or Western medicines. Of all the medicines taken by the children, two thirds were provided or facilitated by adults (assisted treatment) and one third taken by the children themselves without adult involvement (self-treatment). Among boys, the proportion of illnesses, which were self-treated increased with age from 12% in the youngest age group (< 13 years) to 34% in the oldest (> 14 years). In girls, the proportion of illnesses which were self-treated was consistently lower than among boys and remained constant around 9% for all age groups. The proportion of Western pharmaceuticals used for self-treatment increased with age from 44% in the youngest age group to 63% in the oldest (average 52% Western pharmaceuticals). Again, there were differences between boys and girls: among the youngest age group, boys were twice as likely to use pharmaceuticals than girls (62 versus 32% of the self-treatments, respectively) and in the oldest age group they were nearly three times more likely (75 versus 25%, respectively). These differences in self-treatment practices and choice of medicines between girls and boys may reflect the higher income potential of boys, who can earn money by fishing. Pharmaceuticals were generally preferred for the treatment of headache and fevers, or colds, while herbal remedies were the preferred choice for the treatment of abdominal complaints and wounds. The most commonly used pharmaceuticals were antimalarials (mainly chloroquine), painkillers and antipyretics (mainly aspirin and paracetamol), which were stocked in most small shops in the village at low prices and readily sold to children. Throughout primary school age Kenyan children are growing into a pluralistic medical practice, integrating Western pharmaceuticals into the local herbal medical system, and gradually become autonomous agents in their health care.