Twelve patients had undiagnosed articular disease associated with type IV hyperlipoproteinemia. Objective joint findings involved both large and small joints. Disease was bilateral but asymmetrical and oligoarticular. Synovitis was mildly inflammatory and persistent rather than episodic in nature, and disability was minimal. Serial clinical, laboratory, and radiographic assessment excluded other currently recognized forms of rheumatic disease. Joint radiographs demonstrated large metaphyseal and epiphyseal cysts in five patients. Synovioanalysis and synovial biopsy results are reported in two patients. These cases appear to constitute a clinically homogeneous group. The concurrence of a distinctive articular syndrome and type IV hyperlipoproteinemia suggests a possible causal relationship.