This study investigated the association between psychosocial stress and outcome of in-vitro fertilization and gamete intra-Fallopian transfer treatment. Ninety women, enrolled for treatment at a private infertility clinic, completed two self-administered psychometric tests (Bi-polar Profile of Mood States, POMS; and State-Trait Anxiety Inventory, STAI) and a questionnaire to ascertain demographic and lifestyle characteristics before the start of treatment. Approximately 12 months later an outcome measure was determined for each participant in terms of whether she was pregnant or not pregnant and the number of treatment cycles undertaken to achieve clinical pregnancy. The women's scores on the psychological tests were similar to published normative scores. On univariate analysis, history of a previous pregnancy was positively related to the probability of pregnancy and full-time employment, a more 'hostile' mood state and higher trait anxiety were associated with a lower cumulative pregnancy rate. A Cox multiple regression model found previous pregnancy history, trait anxiety, and the POMS agreeable-hostile and elated-depressed scales to be the most important lifestyle and stress variables predictive of pregnancy. The results emphasize the importance of psychosocial stress in treatment outcome but indicate that the relationships are complex. Further studies are required to validate whether these findings can be generalized to other populations.