This paper reports on an evaluation of a domestic violence intervention in the maternity and sexual health services of a UK hospital. The intervention encompassed guidelines, staff training, inclusion of routine enquiry for domestic violence with all patients, and referral of women disclosing violence to an on-site advocacy service. An "assumption querying" approach was applied to evaluate the intervention. Programmatic assumptions were identified and tested using interviews with service providers and patients, review of patient records, and pre- and post-training questionnaires. Domestic violence training resulted in changes in health professionals' knowledge and practice in the short-term, but universal routine enquiry was not achieved even in a context of organisational support, guidelines, training and advocacy. Potential and actual harm occurred, including breaches of confidentiality and failure to document evidence, limiting women's ability to access civil and legal remedies. Advocacy support led to positive outcomes for many women, as long as support to maintain positive changes, whether women stayed with or left the violent partner, continued to be given. Maternity and sexual health services were found to be opportune points of intervention for domestic violence services that combine routine enquiry by clinicians, support after disclosure and attention to harm reduction.