Radiological evidence of osteoarthrosis has been studied in the distal and proximal interphalangeal and metacarpophalangeal joints of 265 old people living at home. Intra- and inter-observer variation was found to be in general satisfactory for the grading system used. In the distal interphalangeal joints the mean grade of osteoarthrosis was greatest in the index and middle fingers, was greater in women than in men, and increased with age in both sexes. The pattern in the metacarpophalangeal joints was similar, but there was no preferential involvement in the proximal interphalangeal joints. Increasing mean grade of involvement of proximal interphalangeal joints was associated with increasing involvement of distal interphalangeal and metacarpophalangeal joints, independently of age or sex. There was no significant variation in severity of osteoarthrosis with occupation in men, nor any association with bone rarefaction in either sex. The findings are discussed with particular reference to recently advanced hypotheses about the pathogenesis of osteoarthrosis.