The present study reports a DSC investigation of solid-liquid equilibria in the o-acetylsalicylic acid-caffeine binary system revealing a simple eutectic behaviour. The eutectic temperature and temperatures of liquidus were determined. Further, assessed eutectic and liquidus temperatures together with the data for pure components were used for the evaluation of the Redlich-Kister equation parameters for the excess Gibbs energy of binary melts. The binary T-x phase diagram of the above mentioned system was calculated using the FactSage software and the ternary eutectic in the system o-acetylsalicylic acid-caffeine-paracetamol was predicted.