The authors compared demographic and clinical data in patients with spondylarthropathy residing in Morocco or in France and searched for factors associated with increased disease severity, with special attention to course of the disease, life style, clinical findings and roentgenographic changes. They carried out univariate analyses (chi-square test, Student's t test) to look for factors associated with hip involvement. Evaluation of the relative risk associated with each factor by determination of the odds ratio and corresponding 95% confidence interval. Statistically significant differences were found between the two groups concerning socioeconomic status and disease characteristics. Patients seen in Morocco had more severe disease, with roentgenographic hip involvement in 48% of cases versus only 16% of patients seen in France (p < 0.0001). Several factors were associated with the presence of hip disease, including residence in Morocco, Maghrebine ethnic origin, patient characteristics (male sex, low body mass index), disease characteristics (high erythrocyte sedimentation rate, young age at onset), and environmental factors (no running water in the home). Patients with spondylarthropathy residing in Morocco had more severe disease than their counterparts living in France; both genetic and environmental factors may explain this difference.