Objectives: To validate a self administered postal questionnaire appraising risk of coronary heart disease. To determine whether use of this questionnaire increased the percentage of people at high risk of coronary heart disease and decreased the percentage of people at low risk who had their cholesterol concentration measured. Design: Validation was by review of medical records and clinical assessment. The questionnaire appraising risk of coronary heart disease encouraged those meeting criteria for cholesterol measurement to have a cholesterol test and was tested in a randomised controlled trial. The intervention group was sent the risk appraisal questionnaire with a health questionnaire that determined risk of coronary heart disease without identifying the risk factors as related to coronary heart disease; the control group was sent the health questionnaire alone. Setting: One capitation funded primary care practice in Canada with an enrolled patient population of about 12,000. Subjects: Random sample of 100 participants in the intervention and control groups were included in the validation exercise. 5686 contactable patients aged 20 to 69 years who on the basis of practice records had not had a cholesterol test performed during the preceding 5 years were included in the randomised controlled trial. 2837 were in the intervention group and 2849 were in the control group. Main outcome measures: Sensitivity and specificity of assessment of risk of coronary heart disease with risk appraisal questionnaire. Rate of cholesterol testing during three months of follow up. Results: Sensitivity of questionnaire appraising coronary risk was 87.5% (95% confidence interval 73.2% to 95.8%) and specificity 91.7% (81.6% to 97.2%). Of the patients without pre-existing coronary heart disease who met predefined screening criteria based on risk, 45 out of 421 in the intervention group (10.7%) and 9 out of 504 in the control group (1.8%) had a cholesterol test performed during follow up (P < 0.0001). Of the patients without a history of coronary heart disease who did not meet criteria for cholesterol testing, 30 out of 1128 in the intervention group (2.7%) and 18 out of 1099 in the control group (1.6%) had a cholesterol test (P = 0.175). Of the patients with pre-existing coronary heart disease, 1 out of 15 in the intervention group (6.7%) and 1 out of 23 in the control group (4.3%) were tested during follow up (P = 0.851, one tailed Fisher's exact test). Conclusions: Although the questionnaire appraising coronary risk increased the percentage of people at high risk who obtained cholesterol testing, the effect was small. Most patients at risk who received the questionnaire did not respond by having a test.