Objective To determine the effectiveness of prescribing 2 g plant sterols/stanols per day as an addition to standard practice in a dietary outpatient clinic. Design A randomized parallel design of comparative 12-week interventions. Subjects/Setting Patients referred by a general practitioner to a dietary outpatient clinic for the management of hyperlipidemia were eligible. Twenty-five patients (15 women and 10 men) completed the study. Intervention Counselling regarding diet for hyperlipidemia was based on the National Cholesterol Education Program (NCEP) guidelines. The intervention group was instructed to incorporate ~25 g/day of margarine containing plant sterols/stanols, which delivered ~2 g of plant sterols/stanols. Main outcome measure Changes in diet, body weight and serum total cholesterol, LDL cholesterol, HDL cholesterol and triglycerides. Statistical analysis performed Changes in dietary and biochemical outcomes were assessed using Student’s t-test. For non-normally distributed data, Wilcoxon signed rank test was used and Mann-Whitney U tests were conducted to determine the proportion of subjects reaching defined goals. The number needed to treat (NNT) index was used to report effectiveness of the intervention. Results Five of 14 subjects in the intervention group compared to 0 of 11 in the control group achieved a reduction in serum cholesterol of ≥ 15% (P < .05). Using the NNT index, for each 2.8 patients counselled with routine prescription of plant sterols/stanols, one additional patient would obtain a reduction in cholesterol by ≥ 15% compared with conventional management. This was achieved without any detrimental effects on the dietary fatty acid profile. Application/conclusion Routine prescription of margarine containing plant sterol/stanol is an effective strategy in the management of hypercholesterolemic patients in the clinical setting.