The cause of unilateral sudden sensorineural hearing loss (SNHL) remains unclear in many clinical cases. Perilymphatic leakage through a fissula ante fenestram (FAF) fistula is one possible reason. We present four clinical cases with proven FAF fistula, discovered during surgical exploration. All patients experienced partial hearing recovery after surgical coverage of the fistula. We suggest FAF as a possible site for perilymphatic leakage, representing an anatomical correlate for sudden unilateral SNHL. We recommend early exploratory tympanotomy with special attention to the bony region, anterior to the oval window, in cases of severe sudden SNHL and suspected FAF.