The authors report three cases of type IIa hypercholesterolemia in which ultrastructural observation of the synovial fluid revealed the presence of frothy cells and microcrystals. A questionnaire-based retrospective investigation amongst a population of 201 patients followed-up for type IIa essential hypercholesterolemia revealed the presence of joint disorders in 92 cases (45.8%). The condition sometimes affected a single joint (17.4%), but was generally polyarticular (82.6%), affecting the large joints. Joint pain was reported in 38 cases (41.3% of the patients presenting joint disease and 18.9% of the group as a whole) and predominantly affected the arms. Acute arthritis (54 cases) occurred preferentially in the legs. In 35 cases (38% of the joint-disease cases and 17.4% of the population as a whole) this resulted in acute rheumatic fever. Nineteen of these cases were unspecified forms of arthritis (20.7% amongst the joint-disease sufferers and 9.5% of the population). This analysis, combined with ultrastructural studies of the synovial fluid from 3 patients, establishes the existence of hypercholesterolemic rheumatism amongst heterozygotes as well as amongst homozygotes.