The records of a total of 427 eyes with various types of glaucoma treated by trabeculectomy were compiled from 10 institutions. The follow-up periods of these cases were from 3 months to 5 years. Simple statistics gave an overall success rate of 75% in controlling the intraocular pressure (IOP) below 21 mmHg. In 344 eyes followed more than 1 year, the IOP distribution showed that the IOP was between 14 and 19 mmHg in 47% of th 10 institutions. The follow-up periods of these cases were from 3 months to 5 years. Simple statistics gave an overall success rate of 75% in controlling the intraocular pressure (IOP) below 21 mmHg. In 344 eyes followed more than 1 year, the IOP distribution showed that the IOP was between 14 and 19 mmHg in 47% of th 10 institutions. The follow-up periods of these cases were from 3 months to 5 years. Simple statistics gave an overall success rate of 75% in controlling the intraocular pressure (IOP) below 21 mmHg. In 344 eyes followed more than 1 year, the IOP distribution showed that the IOP was between 14 and 19 mmHg in 47% of the eyes, and in only 2.3% was the IOP lower than 10 mmHg. The probability of failure, i.e. the mean IOP being higher than 20 mmHg for more than 3 months, was calculated by a life-table method, which takes diversity in the follow-up period into account. An analysis of the cumulative failure probability by Weibull distribution function showed that the time course of failure in the IOP control is of an early failure type; the majority of failure occurred within one year. The final failure probability after the follow-up period of 5 years was 0.42 in primary open-angle glaucoma and 0.48 in primary angle-closure glaucoma, but it was 0.65 in congenital glaucoma. It was shown that the failure probability after the first trabeculectomy is lower in the older age group than in the younger age group. The second trabeculectomy on the same eye showed a higher failure probability than the first intervention.