Six cases of endometriosis obstructing the left ureter were observed among 1054 consecutive patients undergoing surgery in an eight‐year period. In addition, 125 women with ureteral endometriosis (left‐sided, n= 66; right‐sided, n= 40; bilateral, n= 19) were described in 62 articles identified in a systematic review of the English language literature between 1980 and 1998. Considering only the patients with unilateral ureteral endometriosis and combining the published figures with those of our surgical series, the observed proportion of left lesions (72/112, 64%; 95% CI 55% to 73%) was significantly different from the expected proportion of 50% (χ2i, 9.14, P= 0.002). The lateral asymmetry found in the location of ureteral endometriosis is compatible with the menstrual reflux theory and with the anatomical differences of the left and right hemipelvis