PURPOSE: Congenital smooth muscle hamartomas are benign tumors composed of proliferating smooth muscle cells. They are usually seen as abnormal patches of skin. Ocular involvement of congenital smooth muscle hamartomas is unusual, with rare reports of patients with external eyelid involvement or proptosis resulting from orbital tumors. We describe a patient with a congenital smooth muscle hamartoma that involved the tarsal conjunctival fornix. METHODS: Review of the patient's medical records, including the results of ophthalmologic, radiologic, and histologic examinations. RESULTS: A healthy 2-year-old boy was initially seen with a conjunctival mass. He had a discrete, gray, cystic-appearing lesion in the inferior fornix of the left eye. A magnetic resonance imaging study revealed no signs of extension of the lesion into the orbit. The lesion was surgically excised. Histologic sections showed large bundles of smooth muscle with a fibrotic background and interdigitating fat, consistent with a diagnosis of a congenital smooth muscle hamartoma. CONCLUSION: To our knowledge, this is the first report of a patient with a congenital smooth muscle hamartoma arising from the conjunctival fornix. It presumably originated from either the smooth muscle of the vascular endothelium or from the capsulopapebral muscle. Congenital smooth muscle hamartoma should be considered in the differential diagnosis of cystic-appearing conjunctival fornix lesions.