The purpose of the work was to investigate: Whether osteoarthritis of the hip can be divided into radiologic classes by examining the tendency of osteoarthritis of the hips to increase the growth and calcific content of the bone on the one hand and the associated loss of calcium and cartilage and the deformation and destruction of bone on the other. The prevalence of osteoarthritis of the hip in the internal medicinal and surgical outpatients of the University Central Hospital of Oulu, who were radiographed. Whether osteoarthritis of the hip or its different radiologic manifestations correlate with the patient's age, sex, occupation and strenuousity of work, rickets, cancerous diseases, diabetes, rheumatoid arthritis, family history, parity, smoking, obesity, physical activity, corticosteroid and anti-epileptic medication, and previous injuries to the lower extremities causing immobilization. Whether the radiologic findings of osteoarthritis of the hip are associated with typical symptoms. Whether there are correlations between the effects of medication and physiotherapy and the radiologic forms of osteoarthritis of the hip. The study population consisted of two series, of which the first included 401 patients: 167 males and 234 females. The second, or major part comprised 518 patients, of whom 249 were male and 269 female. For all these patients we had radiograms available which permitted reliable assessment of the hip condition. The second series, i.e. the latter group of 518 patients, also filled in a questionnaire which dealt with the etiology and symptoms of the osteoarthritis of the hip as well as the therapies they had received. Whenever possible, the changes of the pelvis and the lumbar spine were also assessed on the basis of the radiograms. On the basis of the radiologic findings, osteoarthritis of the hip was divided into two qualitative classes, hypertrophic and destructive, and a mixed type, and into three grades of severity. Hypertrophic osteoarthritis of the hips accounted for 51% of the cases, destructive for 20% and mixed type for 29%. The percentages for the different severities were 47% for the mild, 16% for the moderately severe and 37% for the severe. A total of 26% of the cases were right-sided, 22% left-sided and 52% bilateral. The mild, bilateral cases of osteoarthritis were mostly hypertrophic, whereas destructive osteoarthritis was clearly more common in the unilateral cases. Hypertrophic osteoarthritis was also more frequent in younger age-groups and destructive in older age-groups. The osteoarthritis of the older patients was more severe.(ABSTRACT TRUNCATED AT 400 WORDS)