Background Recent research in the USA and UK indicates that person-centred planning (PCP) can lead to improvements in lifestyle-related outcomes for people with intellectual disabilities (ID). It is clear, however, that the introduction of PCP does not have an equal impact for all participants. The aim of the present paper was to identify factors associated with the probability of delivering a plan and with improvements in outcomes for those who did receive a plan. Methods Information on the life experiences of participants was collected over a period of approximately 2 years for a cohort of 93 adults with ID. Results There were powerful inequalities in both access to and the efficacy of PCP in relation to participant characteristics, contextual factors and elements of the PCP process. Conclusions Results are discussed in relation to implications for policy and practice for increasing the effectiveness of PCP and reducing inequalities in the life experiences of people with ID.