This paper shows the Atlantic Equatorial Undercurrent (EUC) revealed by a PIRATA ADCP during 2002 at 0¿N, 23¿W and simulated by an eddy-resolving ocean general circulation model (MOM) forced by NCEP/NCAR reanalysis wind stresses. The PIRATA data revealed the shallowing of the EUC between January and May, concurrently with the reversal of the easterly trades to westerly, and the deepening of the EUC from May to December. Empiric Orthogonal Function (EOF) analysis shows two main components; the first mode, explaining 63.7% of the total variance, represents the main seasonal variation of the undercurrent during 2002, while the second mode, explaining 19.9% of the variance, represents higher frequency variability occurring in the EUC core, from 60 to 80 m. All model experiments were able to reproduce this variability, and the best one was chosen objectively using EOF and joint EOF analysis techniques.