Background: Nail changes have traditionally been used as diagnostic aids. Their usefulness in general and predictive value in particular, however, is not known. Objective: Our purpose was to survey nail changes and to clarify the potential of nail abnormalities to diagnose nondermatologic diseases. Methods: The fingernails of 567 patients admitted to general medical and surgical wards were examined. The point prevalence rates were calculated on the basis of a binomial distribution. The results were compared with the diagnosis with logistic regression analysis correcting for age and sex. Results: The most common findings were absence of lunulae (22.9% [19.5% to 26.6%]), white nails or apparent leukonychia (11.8% [9.3% to 14.8%]), and red lunulae (5.1% [3.5% to 7.3%]). The following significant associations were noted: pulmonary disease and clubbing (odds ratio[OR] = 4.1, 95% confidence interval [CI] = 1.7 to 9.5), hematologic disease and brittle nails (OR = 4.6, 95% CI = 1.6 to 13.7), hematologic disease and Terry nails (OR = 8.7, 95% CI = 2.7 to 27.0), gastrointestinal disease and pincer nails (OR = 33.6, 95% CI = 3.7 to 307.3), and gastrointestinal disease and subjective complaints (OR = 2.7, 95% CI = 1.4 to 5.0). Conclusion: Several significant associations were identified, suggesting that nail abnormalities can be diagnostic clues in the diagnosis of chronic nondermatologic diseases. An association between pincer nails and gastrointestinal disease has not been previously described.