Homozygous carriage of a 14 base pair (bp) insertion in exon 8 of the HLA-G gene may be associated with low levels of soluble HLA-G and recurrent miscarriage (RM). We investigated the G14bp insertion(ins)/deletion(del) polymorphism in 339 women with unexplained RM and 125 control women. In all patients and patients with secondary RM after a firstborn boy, 19.2% and 23.9%, respectively, were G14bp ins/ins compared with 11.2% of controls (p<0.05 and p<0.01). Among secondary RM patients with a firstborn boy, G14bp del/del and no carriage of an HLA class II (HYrHLA) allele restricting immunity against male-specific minor HY antigens was found less often than in controls (p<0.05) whereas G14bp ins/ins and carriage of HYrHLA predisposed (p<0.08) to this clinical entity. The mean birth weight of firstborn boys born to G14bp ins positive secondary RM patients was significantly lower than expected (p<0.001) but only in carriers of HYrHLA alleles (p<0.01).In conclusion, homozygosity for G14bp ins predisposes to RM. The combination of G14 ins homozygosity and carriage of HYrHLA predisposes to secondary RM in women with a firstborn boy and negatively affects birth weight in these boys.