There are many conditions  affects the nail health, causing increasing incidence of nail diseases. More than 50 percent of these have fungal origion. Laboratory diagnosis and management of fungal nail diseases remain as a medical problem. Fungal infections of the nail are called onychomycosis.  In present series of this manuscript we will discuss on different nail disorders in differential diagnosis with onychomycosis. First of all, anatomy and physiology of the human nail will be reviewed, then pathologic conditions and diseases will be discussed in following issues.