OBJECTIVE The introduction of endonasal laser dacryocystorhinostomy (ENL-DCR) in the early 1990s showed great promise of changing dacryocystorhinostomy into an elegant, minimally invasive procedure from the traditional external dacryocystorhinostomy (EXT-DCR). This prospective, randomized study compares these two operations, their success rates, surgical durations, and postoperative symptoms. METHODS A total of 64 cases in 61 patients with primary acquired nasolacrimal sac or duct obstruction were divided into 2 subgroups by symptoms (simple epiphora and chronic dacryocystitis). These patients were randomized within both subgroups into 2 operation groups with 32 cases in each group. METHODS Altogether, 32 EXT-DCRs and 32 ENL-DCRs were performed. The silicone tube was removed at 6 months after surgery. The final follow-up visit was at 1 year after surgery. The patency of the lacrimal passage was investigated by irrigation, and patients were questioned about their symptoms. METHODS The patency of the lacrimal passage to irrigation and the duration of surgery were measured. RESULTS The success rate at 1 year after surgery was 91% for EXT-DCR and 63% for ENL-DCR after primary surgery. The difference was statistically significant (P = 0.016). The surgical duration for ENL-DCR was three times shorter than for EXT-DCR, the average duration being 23 minutes and 78 minutes, respectively (P < 0.0001). CONCLUSIONS The EXT-DCR, when compared with ENL-DCR, seems to provide superior operation results in primary acquired nasolacrimal duct obstruction.