The isolation of older people is recognised as a major social problem in contemporary Western society. While the risk factors and social or health outcomes of isolation and loneliness in later life are well documented, evidence regarding the effectiveness of programmes aimed at reducing social isolation in older people remains inconclusive. This paper reports on the challenges of attempting to undertake a rigorous evaluation of three demonstration pilot projects targeting older people at risk of social isolation, conducted within different social settings in Queensland, Australia. The demonstration projects were part of the Queensland Cross-Government Project to Reduce Social Isolation in Older People (CGPRSIOP) led by the Office for Seniors within the Queensland Department of Communities. In the absence of good evaluation of programmes aimed at social isolation, this government-run programme incorporated validated psychological measures to evaluate the effectiveness of interventions. While use of these measures suggested some promising results, the focus of this paper is on the methodological and practical challenges associated with utilising evaluation measures in community-based interventions. The detailed consideration of the methodological issues involved in this programme highlights some key lessons and offers new insights into evaluating interventions for reducing social isolation.