This review's purpose is to describe for the practicing clinician the current knowledge about patient compliance to cholesterol-altering drugs and about procedures for compliance management applicable to clinical practice in the United States. Compliance is defined for four commonly measured major steps and, based on recent electronic monitoring data, for three quantitative categories of active medication-taking. The concepts and definition of compliance are undergoing evolutionary changes due to the measurement and availability of new dimensions through electronic monitoring of patient compliance. Substantial non-compliance to cholesterol-altering drugs has been reported in nine large clinical trials for primary and secondary prevention of coronary heart disease, in two HMOs, and, using electronic monitoring of compliance, in one clinical trial and a selected practice. The risks of treatment discontinuation increased continuously during treatment and totaled from 6 to 30% after 5 years. Patterns of day-to-day partial compliance are emerging. Procedures and knowledge for clinical management of compliance are described including methods of measuring compliance, risk factors for non-compliance, standards for compliance performance, epidemiology of compliance, procedures for managing compliance at the start of therapy and for addressing compliance problems during established treatment, simple office assessment of compliance by brief interview questions, compliance aids, prediction of compliance, and education and training of medical-care personnel in compliance management.