BACKGROUND/AIMS: There is a paucity in the literature on the presentation, management and outcomes of cases where primary acquired melanosis (PAM) is associated with spill over/contiguous periocular lentigo maligna (LM). We describe experience of such cases at our eyelid and ocular oncology specialist centre. METHODS: We conducted a retrospective consecutive case review of adult patients with PAM and periocular LM between 2005 and 2024 at Moorfields Eye Hospital in London. Demographic data, diagnosis, histology, imaging, treatment, surgical notes, outcomes and follow-up were collected from the electronic patient record. RESULTS: Of 21 patients identified, 100% were Caucasian, 13 (62%) were women and the average age of diagnosis was 67 years. Grade of PAM atypia was mild in 5 (24%), moderate in 2 (9%) and severe in 14 (67%) patients. 16 (76%) patients developed melanoma (all types) and 12 (57%) patients developed conjunctival melanoma. Of those with PAM with severe atypia, 93% developed melanoma. The average time interval from diagnosis of PAM and LM to melanoma was 72 months. Melanoma recurrence occurred in 7 (44%) and metastases developed in 4 (25%) patients. Four patients died, including two from metastatic melanoma. Average follow-up length was 129 months. CONCLUSIONS: PAM with atypia, particularly severe atypia, when associated with spill over periocular LM, may have significant risk of progression to melanoma. Patients with PAM require careful eyelid examination to identify LM. Management requires multidisciplinary input, urgent biopsy and confocal microscopy if available, lower threshold for treatment and lifelong monitoring.