A simple procedure for determination of trans-resveratrol in wines from Alentejo region delimited appellation (Portugal) is described and validated. A set of 47 red and 21 white wines was analysed by direct injection in high performance liquid chromatograph with UV detector. A detection limit of 0.06 mg/L was achieved. Global uncertainty associated with the results, according to EURACHEM/CITAC rules, ranged from 16.33 to 27.15 %. Trans-resveratrol was detected in all red wines and in 8 white wines. The amount was consistently higher in the red wines (up to 2.64 mg/L), when compared to the white wines (never exceeding 0.19 mg/L).