One hundred thirty-one cases of conjunctival melanoma in which biopsies had been performed were studied to determine potential factors that might affect outcome in patients with these lesions. Two groups of lesions were identified: those associated with primary acquired melanosis (melanoma with PAM, 98 cases, 74.8 per cent) and those without primary acquired melanosis (melanoma without PAM, 33 cases, 25.2 per cent). The overall mortality rate in the 131 cases was 26 per cent (34 of 131); the mortality rate due to melanoma with PAM was 25.5 per cent (25 of 98), and that due to melanoma without PAM was 27.3 per cent (9 of 33). If PAM was associated with the lesion, the presence of atypical melanocytes within the epithelium (pagetoid invasion) was a sensitive indicator of subsequent metastasis. Tumor thickness may also be useful for predicting subsequent metastases. None of the histologic parameters studied proved useful for predicting outcome in patients who had melanomas without PAM. The presence or absence of nevi had no effect on prognosis.