Previous surveys have suggested marked ethnic and geographical variation in the occurrence of joint hypermobility. We investigated the prevalence of joint hypermobility and the influences of age, sex, body mass and occupation in a rural Yoruba population in Nigeria. The study sample consisted of 204 individuals aged 6-66 yr from the townships of Igbo-ora and Eruwa in south western Nigeria. Sixty-eight had reported joint pain as part of a population survey of arthritic disorders and each was age and sex matched with one household and one neighbour control. Joint hypermobility was assessed, at four peripheral sites bilaterally and forward flexion of the trunk, by a single observer using the Beighton score. Each subject had weight and height recorded, answered a brief questionnaire about occupation and joint symptoms and was examined for peripheral joint disease. Only 11 (5%) of the subjects were negative at all five sites whereas 111 (54%) were hypermobile at three or more sites including 23 (11%) positive at all five. Using a score of 4/9 or greater as a cutoff, 88 (43%) were positive, including 35% of males and 57% of females. There was a linear decline with age in females but a more rapid decline only to age 35 yr in males. There was no relation to body mass or occupation. We conclude that joint hypermobility amongst this population is substantially greater than that recorded for other groups but is not associated with joint pain.