The aim of this study was to evaluate the therapeutic efficacy of intravenous immunoglobulin (IVIG) in the prevention of recurrent spontaneous abortion (RSA). In a double-blind, randomized, placebo-controlled study, 41 women with a history of unexplained recurrent spontaneous abortion were treated with IVIG or saline infusions during pregnancy. The birth of a child was considered a successful outcome. The overall success rate was 77% in the IVIG group compared with 79% in the placebo group. For women with primary RSA the success rates were 82 (IVIG) and 89% (placebo), and for women with secondary RSA the rates were 73 (IVIG) and 70% (placebo). We found no statistically significant difference in treatment results between IVIG and placebo.