Guidelines for psychosocial support have been developed, but there are no standard approaches in routine oncology practice to identify patients experiencing social difficulties. We have designed and evaluated a Social Difficulties Inventory (SDI) to identify patients requiring further assessment and, where appropriate, referral to support services. The purpose of this study was to develop a clinically meaningful SDI scoring system with guidance for oncology staff. Out of 189 patients, 183 completed the SDI and were interviewed by a social work researcher who scored the SDI independently. Comparison of patient/interviewer assessment was good (intraclass correlation 0.61, 95% confidence interval: 0.51, 0.70). Using top 10% of interviewer social distress (SD) scores to indicate 'SD case', the best 'cut-point' was a patient score of > or =10 (sensitivity=0.80; specificity=0.76; 56 out of 183 'cases'). Out of 127 patients, 72 with SD score <10 had individual SDI item rated at a higher level. Following interview, 32 patients were referred to specialist services, 46 given information and 112 had no action taken. An interpretation algorithm developed includes SD score, individual SDI item rating, and an additional general question, illustrated using four case scenarios. In conclusion, general guidance for interpreting the SDI has been developed to enhance health-care professional/patient consultations with a view to identifying patients who may benefit from support, advice or intervention.