OBJECTIVE To analyse the unusual physical sign of iris crystals occurring in patients with uveitis. METHODS Demographic details and clinical features were documented in 24 patients with chronic uveitis and iris crystals. Plasma immunoglobulin subclasses were measured, and a histopathological review of iridectomy specimens from 33 patients with chronic uveitis was also undertaken. RESULTS The mean age of patients was 38 years, with a slight preponderance of females. 17 patients had Fuchs' heterochromic cyclitis although a number of other uveitis entities were represented. There was no correlation between severity of clinical signs and presence of iris crystals. Over a mean follow up period of 15 months no significant change in the number, size, or position of the crystals was seen except in four patients who underwent intraocular surgery. Only three patients had raised plasma IgG1. The review of the histology of iridectomy specimens failed to show evidence of Russell body formation in any patient. CONCLUSIONS Iris crystals appear to be rare but may be underreported as they are small and can easily be missed. They are likely to be associated with disease processes in which there is active immunoglobulin production within the anterior chamber, such as Fuchs' heterochromic cyclitis.