Background: Personality differences between surrogate mothers (SMs) who gestate and relinquish and intended mothers (IMs) who commission a genetically related or unrelated baby have been unexplored in the UK. Furthermore, the psychological effects of the arrangement have not been determined in a prospective longitudinal study, making this the first quantitative report of psychological functioning in SMs and IMs. Methods: SMs and IMs (n = 81: 61 surrogate, 20 intended) undergoing genetic or gestational surrogacy (4 groups) were assessed by postal questionnaire during the first, second and third trimesters of pregnancy. Those with a positive outcome were assessed again in the first week, at 6 weeks and 6 months post-delivery of the surrogate baby. Results: There were no significant differences between or within SM andIM groups on personality characteristics. Social support, marital harmony and state anxiety differed significantly (to P < 0.01) between SMs and IMs at different stages of the arrangement. Differences in attitudes towards the pregnancy and the baby were also observed between groups during pregnancy (to P < 0.001), but there was no evidence of post-natal depression amongst the groups studied. Conclusions: These results are important because they demonstrate psychological effects of the surrogate arrangement are notable and occur over an extended period of time. It also shows that psychological screening and support prior to, during and following surrogacy is indicated.