Recognition that informal cancer carers experience unmet needs and psychological distress has led to the development of a range of psycho-social interventions. The efficacy of such interventions is examined through a systematic review of the research literature, following National Health and Medical Research Council and Cochrane Collaboration guidelines. Of 13 level II randomised controlled trials (RCTs), only eight showed significant differences across groups, with moderate effect size. This included improvement in caregiver experience or appraisal of caregiving following psycho-education (two studies); improved sexual satisfaction, dyadic coping, relationship quality and communication, or reduced psychological distress, following couple counselling (4); reduced distress following family grief therapy (1); and reduction in distress in bereavement following home palliative care (1). Level III and IV studies were also reviewed, reporting positive effects of psycho-education (5), problem solving (3), an arts intervention (1) and a support group (1). However, methodological concerns limit the generalisability of findings of level III and IV studies. It is concluded that interventions should target those most in need of support; recognise specific needs of carers across cancer type and stage, gender and relationship context; be theory based; and evaluations should utilise RCT designs with outcome measures appropriate to the specific aims of the intervention, rather than global measures of distress.