A novel, fast, and sensitive stability-indicating HPLC method was developed, fully validated, and applied to the simultaneous determination of aliskiren and hydrochlorothiazide in a combined formulation. Effective chromatographic separation was achieved using a phenyl analytical column with isocratic elution using the mobile phase 0.030 M ammonium acetate-acetonitrile (60 + 40, v/v) at a flow rate of 0.40 mL/min. The UV spectrophotometric detector was set at 280 nm. The method was linear over the concentration ranges of 1.5-4.5 and 0.125-0.375 μg/mL for aliskiren and hydrochlorothiazide, respectively. The intraday and interday RSD values were less than 6.1%, while the relative percentage error, Er, was less than 5% for both analytes. Both drugs were subjected to stress conditions of acidic and alkaline hydrolysis, oxidation, and thermal degradation. The proposed method proved to be stability indicating by resolution of the drugs from their forced degradation products. The method was applied successfully to the QC and content uniformity tests in combined commercial tablets.