OBJECTIVES: Chlorthalidone (CLD) and hydrochlorothiazide (HCTZ) are the two most widely used thiazide-type diuretics. This study compared patient characteristics for CLD and HCTZ. METHODS: Adult patients with a hypertension diagnosis (ICD-9 401-405) and ≥2 antihypertensive prescriptions, one of which is CLD or HCTZ, were identified in the MarketScan Databases (2003-2009). Patients switching from CLD to HCTZ, or vice versa, or taking both together were excluded from the study. Patients had continuous enrollment for ≥6 months prior to and after their first prescription of either study drug RESULTS: A total of 15,219 and 890,272 patients were identified for the CLD and HCTZ groups (female: 52.0% vs. 55.2%, mean age: 59.7 vs. 58.6 years). Notably different rates (CLD vs. HCTZ) were observed for prior medical conditions gout (3.4% vs. 2.4%) and chronic kidney disease (6.2% vs. 3.6%), with less pertinent differences for coronary heart disease (17.1% vs. 15.3%), congestive heart failure (11.0% vs. 10.0%), arrhythmia (12.5% vs. 11.2%), hyperlipidemia (46.7% vs. 44.0%) and diabetes (21.2% vs. 19.3%). The mean Charlson Comorbidity Index (CCI) scores for CLD group were 3.3 and 3.1 for HCTZ group. Higher proportions of CLD patients had previously used beta blockers (BB) (40.2% vs. 27.8%) and calcium channel blockers (CCB) (27.7% vs. 21.8%), a lower proportion had used angiotensin receptor blockers (ARB) (12.9% vs. 16.0%), and similar use was seen for angiotensin-converting enzyme inhibitors (ACEI) (25.9% vs 25.2%). CLD patients had higher rates of concurrent BB (33.9% vs. 23.3%) and CCB (24.3% vs. 17.8%) use. Slight differences in the rates of ARB (12.6% vs. 10.9%) and ACEI (22.3% vs. 21.0%) concurrent use were also observed. CONCLUSIONS: This research suggests similar patient profiles for CLD and HCTZ users with CLD users having a slightly more severe overall prior co-morbidity status and higher rates of prior and concurrent BB / CCB medication use.