Tissue breakdown and exposure of a hydroxyapatite implant were observed in eight patients: in four of six patients after evisceration and in four of 31 after enucleation. The reasons for evisceration were a blind, painful eye and endophthalmitis in two patients each. The reasons for enucleation were a choroidal melanoma in two patients and endophthalmitis and irreparable traumatic damage in one patient each. The patients with endophthalmitis received the implant in a second surgical procedure after intensive antibiotic treatment. Small tissue defects healed spontaneously, whereas large defects showed little tendency to heal by secondary intention. Tissue breakdown over a hydroxyapatite implant may be related to delayed ingrowth of fibrovascular tissue, and possibly related to an inflammatory reaction incited by the hydroxyapatite. Careful case selection, facilitation of tissue penetration by drilling holes into the hydroxyapatite sphere, delayed fitting of the prosthesis, and vaulting of the posterior surface of the initial prosthesis to reduce pressure on the tissues covering the anterior pole of the implant may alleviate the problems of tissue breakdown and exposure.