Allogenic lymphocyte immunotherapy (LIT) as a treatment for unexplained recurrent spontaneous abortion (URSA) is still controversial due to the lack of enough controls to evaluate its effectiveness. Eighteen randomized, placebo-controlled trials with LIT for URSA were included in the meta-analysis. Live birth rates for each group were extracted, and the overall odds ratio (OR) for LIT was calculated. The success rate of treatment group was significantly higher (OR 3.74, 95% CI 3.07 similar to 4.57). LIT performed before and during pregnancy had dramatically improved the live birth rate in women with URSA (OR 4.67, 95% CI 3.70 similar to 5.90). The overall OR was 5.25 (95% CI 4.16 similar to 6.64), which supports a low dose of lymphocytes for treating URSA. Our results indicate that LIT provides a significantly beneficial effect over placebo for URSA. LIT given before and during pregnancy is superior to LIT given only before pregnancy, and the lower doses per treatment (less than 100 x 10(6) lymphocytes or 100 mL peripheral blood) achieved a better outcome.