Retrograde ejaculation as a complication of anterior interbody lumbar fusion was investigated. The diagnosis of retrograde ejaculation was made on the basis of interviews. Patients were informed of the risk of retrograde ejaculation preoperatively. At the follow-up study the patients were asked if they had noticed retrograde ejaculation after their operation. In one case (anejaculation) testis biopsy and vasography was performed. On average, the incidence of retrograde ejaculation as a complication of anterior interbody lumbar fusion has been very low, ranging from only a few cases up to 5.9% of cases involving male patients. We studied 40 male patients with severe low back pain retrospectively after they had undergone anterior interbody lumbar fusion. The mean age at operation was 31.9 years and the mean follow-up time 5.0 years. Retrograde ejaculation occurred after anterior interbody fusion in nine patients. Permanent retrograde ejaculation developed in seven of these patients (17.5%). These patients were all operated on using a transabdominal approach. Major bleeding during the operation (over 2500 ml) was observed in two patients. Seven patients with retrograde ejaculation had undergone a two-level operation (L4-SI), and eight patients had undergone between one and three previous spine operations. Retrograde ejaculation has been underestimated as a complication of anterior interbody fusion in multioperated low back patients. The possibility of this complication should be kept in mind when planning a transabdominal approach for interbody lumbar fusion in male patients. We do not recommend the transabdominal approach in male patients because of the risk of retrograde ejaculation.