When prescription drugs are taken in the correct dose and the correct manner, they have great potential for improving the quality of medical care, but inappropriate and incorrect administration of these drugs can lead to severe health problems. Risk factors for problems related to prescription drug compliance were examined in a cross-sectional retrospective study (n = 1017) of ambulatory individuals who had undergone a Brown Bag Prescription Evaluation Program consultation. A pharmacist interviewer assessed drug-related problems such as duplication of drug product, overutilization and underutilization of medication, drug interactions, and side effects. Associations between specific medication-related problems and patient characteristics (demographics, medical history, and insurance status) were studied. Factors that appear to be associated with compliance problems include a patient's level of understanding of both medication instructions and the drug therapy, length of time since last physician visit, length of time on medication, total number of medications, and number of drug allergies. The class of medication taken was also found to be a significant predictor of excess risk. The age and sex of an individual appear to have little association with the development of compliance-related problems. The study reinforces the need for frequent patient contact with a health care professional and the value of educating the patient about the medication regimen.