A 66-year-old white woman had had a 20-year history of flat primary acquired melanosis involving the left inferior forniceal and palpebral conjunctiva. Over the ensuring 12 years, the patient experienced multiple recurrences of invasive malignant melanoma that emerged from the progressive primary acquired melanosis. Two of these recurrences were composed of nonpigmented spindle cells, and in the most florid invasive malignant melanoma that developed, the spindle cells formed a nodule 7.5 mm thick. The spindle cells were organized into fascicles and small bundles, the latter separated by a loose stroma that was devoid of mucopolysaccharides. The fascicular and neuroidal features in this case were sufficiently well developed to suggest the incorrect diagnosis of a neural tumor or a neurofibroma. However, the presence of intraepithelial atypical melanocytes at the edge of the spindle cell lesion, the absence of mucopolysaccharides in the stroma, the mitotic activity, and the absence of intercellular reticulin fibers favored the diagnosis of a spindle cell invasive malignant melanoma. This morphologic variant of conjunctival melanoma is compared with related cutaneous lesions of melanoma featuring a spindle cell population.