In November 2004, an adult male siamang (Hylobates syndactylus) from The Tisch Family Zoological Gardens-Jerusalem Biblical Zoo (Israel) presented with skin lesions on various body parts. Lesions consisted of alopecia and dry, crusty areas of hyperkeratosis. A diagnosis of dermatophytosis due to Microsporum canis was determined by fungal culture of skin scraping taken from the edge of several lesions. Treatment with various oral and topical antifungal agents such as griseofluvin, itraconozole, and lufenuron resulted in the resolution of most lesions and a decrease in size of the single remaining lesion, which continued to be culture positive for M. canis. The animal was anesthetized and an experimental sustained-release clotrimazole varnish was painted directly on the lesion. Initially there was no change in the lesion, and 2 months later a slightly altered formula was applied under anesthesia. One month later, the lesion began to reduce in size; 3 months after the start of treatment, although 2 years after the onset of clinical signs, the lesion resolved. Minimizing the number of treatments is always an advantage when dealing with exotic animals or zoological collections.