Changes in the annual drug utilization of a cohort of 828 low income Kaiser Foundation Health Plan members in the Oregon region over a four-year period are examined. The study also attempts to identify relationships between consistency in the levels of annual drug utilization and characteristics of the cohort, prescriptions received and doctor office visits (DOVs). The results show no change in the: 1) annual prescription rate; 2) types of drugs received each year; 3) annual DOV rates; and 4) annual prescribing rate by physician specialties. There was consistency in the annual drug and DOV utilization rate among the cohort through time. Consistency in the level of drug utilization was not always directly related to consistency in the level of DOV utilization. Consistent high users of drugs, while few in number (4.6 per cent), received a large proportion (37.3 per cent) of all prescriptions. A substantial proportion (15.8 per cent) of the cohort were consistent nonusers of drugs. Consistency in the level of drug use was related to: sex and age, purpose (disease classification) of the DOVs, the types (new or refill) of prescriptions received, the therapeutic classes of drug received, the number of prescribing physicians and the number of pharmacies patronized.