Late infection of filtering blebs and endophthalmitis are hazardous complications of glaucoma filtering surgery frequently associated with bleb failure and loss of functional vision. To determine possible risk factors for the development of these complications, characteristics of nine eyes of nine patients after filtering surgery in whom late endophthalmitis developed were compared with those in patients who had received a comparable operation at the same time in whom endophthalmitis did not develop. An average of 7.7 +/- 6.2 years (range, 6 months to 18 years) elapsed between the time of the filtering procedure and the initial appearance of endophthalmitis. Factors associated with increased risk were: increased axial length, thin and leaky bleb, conjunctivitis, upper respiratory infection, and the winter season.