OBJECTIVES: The literature contains a plethora of articles on medication compliance research, however, no "gold standard" in the measurement of compliance has been established. The Stage of Change (SOC) construct measure from the Transtheoretical Model of behavioral change has recently been validated in medication compliance. The objective of this study is to compare the SOC measure against FOUR other validated compliance measures in patients being treated for diabetes, hypertension, hypercholesterolemia, hypothyroidism, and hormone replace therapy. METHODS: A total of 171 male and female patients in five primary care physician offices in the state of Georgia, USA, completed a face-to-face questionnaire consisting of the SOC measure, the Medication Adherence Scale, the Medication Outcomes Survey (MOS) compliance question, the Brief Medication Compliance Questionnaire (BMQ) and sociodemographic information. Pharmacy refill records (RR) were collected as the fifth compliance measure. RESULTS: Pearson correlations ranged from a low of 0.09 between RR and BMQ to a high of 0.79 between SOC and MOS. All other correlations ranged between 0.20 and 0.49. All correlations proved significantly different than zero (p<0.05) with the exception of the RR and BMQ correlation. CONCLUSIONS: The majority of correlations between validated measures of compliance ranged from weak to moderate in strength. Therefore the results of this study show selection of a useful compliance measure is difficult. The study findings emphasize that assessing medication-taking behavior of patients and comparing the results of different compliance studies is problematic. The development of valid and reliable measures for compliance behavior is still needed.