In a prospective study, we evaluated the sensitivities of direct microscopy using potassium hydroxide 10% wet-mount preparations and culture for definitive diagnosis of keratomycosis in 171 clinically suspected fungal corneal ulcers. Although cultures were positive in 88 eyes (51.46%), the fungus could be demonstrated by KOH preparation in 94.3% (83 of 88) of the culture-proved cases and 93.6% (160 of 171) of the overall eyes. Direct microscopic examination of a KOH wet-mount preparation is a rapid, reliable, and superior technique of laboratory diagnosis. It is particularly important for the early initiation of antifungal treatment in mycotic keratitis.