Background: Previous authors have claimed that dehydration of the nail plate causes brittle nails. Some experts claim that normal nails contain 18% water, and brittle nails contain less than 16%. Objective: We sought to test the hypothesis that brittle nails contain 2% less water than normal nails. We also examined the relationship between a number of health and behavioral variables and brittle nails. Methods: In all, 102 participants with either brittle or normal nails had two nails clipped and then analyzed for water content by a blinded investigator in the laboratory. Participants filled out a detailed questionnaire designed to reveal information about health and behavior. Results: The mean water content for normal nails was 11.90% and for brittle nails was 12.48%. There was no statistically significant difference between the two groups. The odds of having brittle nails was 3.23 times greater among participants who received a professional manicure (95% confidence interval 1.21, 8.59). The frequency of professional manicures was associated with the likelihood of having brittle nails. Frequency of hand moisturizer use was significantly associated with nail brittleness (95% confidence interval 1.35, 32.10). Family history was significantly associated with the likelihood of having brittle nails (95% confidence interval 1.65, 21.11). Limitations: Analyzing nails from living participants is limiting because samples can only be collected from the distal unattached nail plate. A small subanalysis was performed and showed that the nails were losing water between the time of clipping and laboratory analysis. Therefore, our water percentage results may not be representative of in vivo nail plate water contents. Conclusions: There was no significant difference in water content of brittle compared with normal nails.