The frequency of functionally relevant mutations of the leukaemia inhibitory factor (LIF) gene in infertile women is significantly enhanced in comparison with fertile controls. The objective of this retrospective cohort study was to evaluate the impact of LIF gene mutations on the outcome of the treatment in women with various causes of infertility. Fifteen infertile women with the G to A transition at position 3400 leading to the valine to methionine exchange at codon 64 were analysed. Group A was made up of women with diagnoses that are frequently accompanied by changes in humoral as well as cell-mediated immunity - idiopathic infertility and endometriosis (N = 7). Group B consisted of patients with polycystic ovary syndrome (PCOS), andrological factor, tubal factor and hyperprolactinaemia (N = 8). The control group comprised 136 infertile women with no LIF gene mutation diagnosed with idiopathic infertility and endometriosis (N = 37) (group C) and patients with PCOS, tubal and andrological factor (N = 99) (group D). Seven of the mutation-positive patients were successfully treated by in vitro fertilization (IVF), but nobody in this group was diagnosed with idiopathic infertility and only one with endometriosis, which means that there is a statistically significant difference in the pregnancy rates between groups A and B (P = 0.01, Fisher's 2 by 2 exact test) but no statistically significant difference when comparing patients with the LIF gene mutation (group A+B) to no LIF gene mutation (group C+D). The results suggest that in mutation-positive women the idiopathic infertility and endometriosis have a negative impact on the outcome of IVF treatment.