Sebaceous adenocarcinoma (meibomian gland cancer) can be localized at times to one specific area of the eyelid; at other times, it spreads diffusely by pagetoid invasion throughout the conjunctiva. The pagetoid spread is often impossible to visualize. I used a map biopsy of the conjunctiva to determine the extent of involvement of sebaceous adenocarcinoma in 12 patients. Sixteen conjunctival biopsy specimens were taken from various areas of the palpebral and bulbar conjunctiva. An analysis of these specimens helped to delineate the area of tumor involvement, which aided in determining whether to treat these cases by full-thickness eyelid resection or orbital exenteration.