OBJECTIVE.- New advances in health care have shifted concern from infectious to chronic illnesses and therefore a new emphasis in the assessment of satisfaction with pharmacological treatment has risen. A new generic questionnaire to measure Satisfaction with medicines is under construction. Item reduction and factorial validity are discussed here. METHODS.- The initial instrument was composed by 36 items, arranged in 6 dimensions: 1- Efficacy and symptom relieve (5 items), 2- Ease and convenience (6 items), 3- Impact on HRQoL (4 items), 4- Satisfaction with Medical Care (4 items), 5- Medication Side Effects (8 items), and 6- Overall satisfaction (9 items). Items and dimensions where extracted from review of previous English instruments, a panel compose by 8 experts, and 4 focus groups with chronic patients. A convenience sample of 156 patients was used, representative of 7 prevalent chronic pathologies (Diabetes type II, Hypertension, Osteoarthritis, Prostate problems, EPOC/Asthma, Depression, and Migraine). Classic psychometric theory item analysis techniques, exploratory factor analysis, and confirmatory factor analysis (to estimate accurately factor correlations) were applied. RESULTS.- The questionnaire was reduced to a new version of 5 dimensions assessed by 14 items, plus a dimension of Satisfaction with Medication Side Effects (3 items) to be corrected separately due to an important floor effect. The reduced version presents an overall Cronbach alpha of 0.881, acceptable goodness of fit indexes, and all factor loadings are significant (p<0.001). Dimensions are well formed and correlate in different degrees, but the dimension of Satisfaction with Medical Care shows a relevant relation only with Impact on HRQoL (r = 0.45). CONCLUSION.- The questionnaire shows good reliability and validity properties. The 5+1 proposed dimensions are stable and well defined in a 17-item form. Results support that the questionnaire can be used to compute an overall meaningful score.