A sensitive and efficient diagnostic strategy is needed to confirm the clinical suspicion of onychomycosis. The purpose of this study was to compare the sensitivity of three most commonly used diagnostic methods for onychomycosis. Nail specimens of 96 patients with clinically suspected onychomycosis were evaluated using potassium hydroxide smear, culture and histology. A positive result of any of these tests was considered confirmatory for fungal infection and the sensitivity of each test as well as various combinations of them was calculated. The diagnosis of onychomycosis was confirmed in 47 patients (48.9%). Histology was the most sensitive single test for the diagnosis of onychomycosis, although its sensitivity (80.8%) was not statistically different from smear (76.5%). Both histology and smear were significantly more sensitive than culture (53.2%). The most sensitive combination of tests, smear plus histology, was 97.8% sensitive with 98% negative predictive value. In conclusion, direct smear combined with histological examination is the most sensitive diagnostic approach for onychomycosis.