OBJECTIVE: Patient compliance is an important component in the successful management of any disease. In general, it is assumed that in disease states involving periodic, intense pain, such as angina pectoris (AP), compliance rates would be high, and unaffected by dosing regimen. We verified this hypothesis by examining the compliance rates of patients taking different formulations (o.d. (200-300mg), b.d. (90-120mg) and t.d.s. (60mg)) of diltiazem (princeps) for AP. METHOD: We performed a retrospective analysis of 3455 electronic patient records with a diagnosis of AP and a prescription of diltiazem (princeps) from June 1st 1997 to June 1st 1998 (Mediplus-IMS Health) with a one-year follow-up. The above patient cohort was then divided into 3 subgroups according to the different formulation taken. The two subgroups b.d. and t.d.s. were paired to the third one, according to 4 criteria: age, sex, disease history and co-morbidities. Compliance was assessed using initial prescription and refill rates ((pills dispensed/daily dose) / duration of therapy). RESULTS: The proportion of patients showing "good compliance" ( > 0.8) was significantly higher for the o.d. versus b.d. (36.1% versus 25.9%, p=0.001) and for the o.d. versus t.d.s. (36.1% versus 27.1%, p=0.008). We observed the same trend when we compared the mean rate of compliance for the o.d. versus b.d. (0.62 versus 0.55, p=0.0027) and for the o.d. versus t.d.s. (0.62 versus 0.60, p=0.0121). CONCLUSION: Even for life threatening cardiac disease like AP, dosing regimens have a significant effect on compliance. Giving diltiazem as an o.d. formulation could significantly improve compliance and potentially decrease healthcare resources used.