Many nail abnormalities have traditionally been described in association with rheumatoid arthritis (RA), but their specificity has never been assessed in a controlled study. Our purpose was to evaluate the frequency and the specificity of nail changes associated with RA in a case-controlled study including 50 patients suffering from RA and 50 controls. For each patient, a general skin examination was performed and the 20 nails were examined. The nail features were noted and classified. A chi 2 test or a Fisher test was used to compare the two groups. The only nail abnormalities significantly associated with RA were longitudinal ridging on nine or 10 finger nails (29 patients in the RA group vs. three in the controls, chi 2: P < 0.001) and clubbing on at least one nail (24 patients vs. 10, chi 2: P < 0.01). Other nail changes were noticed but were not frequent enough to be significant. The presence of longitudinal ridging on the finger nails was significantly associated with RA.