Asymmetric gait nail unit syndrome (AGNUS) is the result of asymmetric shoe pressure on the toes and foot caused by ubiquitous uneven flat feet that affect the gait. The pressure produces clinical changes in the toenails, which are identical to all clinical types of dermatophyte and opportunistic onychomycosis, yet they are dermatophytes-free. AGNUS produces additional signs that make it easy to identify. Its coexistence with fungal disease has resulted in reports describing new clinical types of onychomycosis, identifying signs of drug resistance, assessing severity index, and defining complete clinical cure when taking a systemic or topical antifungal, as well as "retronychia." These signs are typically seen in the toenails of patients with AGNUS. AGNUS has a mechanical etiology and can coexist with dermatophytosis, which is a hereditary disease. AGNUS can coexist with any other disease affecting the toenails and results in greater clinical severity than each condition individually. AGNUS is and has been the most common worldwide toenail abnormality in shoe-wearing societies.