BACKGROUND: The objective of this study was to develop and psychometrically evaluate a general measure of patients' satisfaction with medication, the Treatment Satisfaction Questionnaire for Medication (TSQM). METHODS: The content and format of 55 initial questions were based on a formal conceptual framework, an extensive literature review, and the input from three patient focus groups. Patient interviews were used to select the most relevant questions for further evaluation (n = 31). The psychometric performance of items and resulting TSQM scales were examined using eight diverse patient groups (arthritis, asthma, major depression, type I diabetes, high cholesterol, hypertension, migraine, and psoriasis) recruited from a national longitudinal panel study of chronic illness (n = 567). Participants were then randomized to complete the test items using one of two alternate scaling methods (Visual Analogue vs. Likert-type). RESULTS: A factor analysis (principal component extraction with varimax rotation) of specific items revealed three factors (Eigenvalues > 1.7) explaining 75.6% of the total variance; namely Side effects (4 items, 28.4%, Cronbach's Alpha =.87), Effectiveness (3 items, 24.1%, Cronbach's Alpha =.85), and Convenience (3 items, 23.1%, Cronbach's Alpha =.87). A second factor analysis of more generally worded items yielded a Global Satisfaction scale (3 items, Eigenvalue = 2.3, 79.1%, Cronbach's Alpha =.85). The final four scales possessed good psychometric properties, with the Likert-type scaling method performing better than the VAS approach. Significant differences were found on the TSQM by the route of medication administration (oral, injectable, topical, inhalable), level of illness severity, and length of time on medication. Regression analyses using the TSQM scales accounted for 40-60% of variation in patients' ratings of their likelihood to persist with their current medication. CONCLUSION: The TSQM is a psychometrically sound and valid measure of the major dimensions of patients' satisfaction with medication. Preliminary evidence suggests that the TSQM may also be a good predictor of patients' medication adherence across different types of medication and patient populations.