Background: Disadvantaged groups are an important target for smoking cessation intervention. Smoking rates are markedly higher among severely socially disadvantaged groups such as indigenous people, the homeless, people with a mental illness or drug and alcohol addiction, and the unemployed than in the general population. This proposal aims to evaluate the efficacy of a client-centred, caseworker delivered cessation support intervention at increasing validated self reported smoking cessation rates in a socially disadvantaged population. Methods/Design. A block randomised controlled trial will be conducted. The setting will be a non-government organisation, Community Care Centre located in New South Wales, Australia which provides emergency relief and counselling services to predominantly government income assistance recipients. Eligible clients identified as smokers during a baseline touch screen computer survey will be recruited and randomised by a trained research assistant located in the waiting area. Allocation to intervention or control groups will be determined by time periods with clients randomised in one-week blocks. Intervention group clients will receive an intensive client-centred smoking cessation intervention offered by the caseworker over two face-to-face and two telephone contacts. There will be two primary outcome measures obtained at one, six, and 12 month follow-up: 1) 24-hour expired air CO validated self-reported smoking cessation and 2) 7-day self-reported smoking cessation. Continuous abstinence will also be measured at six and 12 months follow up. Discussion. This study will generate new knowledge in an area where the current information regarding the most effective smoking cessation approaches with disadvantaged groups is limited. Trial registration number. ISRCTN: ISRCTN85202510.