Carers of people experiencing a first episode of psychosis are at an increased risk of developing their own physical and mental health problems. Psychoeducation has been found to improve carer wellbeing and reduce distress. However, few psychoeducation interventions have considered the resource constraints on mental health services and the impact that these can have on the implementation of any such interventions. The present service evaluation aimed to evaluate an abbreviated version (sole session) of a previously tested psychoeducation intervention (three sessions) that targets less adaptive illness beliefs (n = 17). Pre–post effect sizes reveal that all of the carers’ illness beliefs changed in the desired direction, with four out of the 10 illness beliefs associated with large to moderate improvements. When compared with the outcomes obtained in our evaluation of the more intensive, three-session version of the intervention, the between-group effects largely favoured the three-session version but were mostly small. Moderate to large effects in favour of the three-session version were found for two of the 10 illness beliefs. These findings support the further investigation of the sole session psychoeducation intervention as part of a randomised controlled trial.