In the advanced phase of Parkinson's disease (PD), high frequency electrical stimulation (HFS) of the subthalamic nucleus (STN) can represent a good therapeutic option, whose effects on walking have been recently quantified by kinematic and dynamic gait analysis. The goal of the present study was to compare, in a group of PD patients, the effects of STN stimulation and of L-dopa on trunk kinematics during walking. The additive effect of these two treatments was investigated as well. Ten idiopathic PD patients implanted bilaterally with a STN stimulation system and ten age-matched controls were studied using a three dimensional motion analyser. Four conditions were considered: with (s+) and without (s-) STN stimulation and with (m+) and without (m-) L-dopa administration. The results showed that both stimulation alone and L-dopa alone significantly increased the stride length and the gait speed, with an additional effect if applied simultaneously. Cadence was more influenced by L-dopa. The range of lateral bending and torsion of the trunk, which were reduced in s-/m-, increased similarly in s-/m+ and in s+/m- conditions. The exaggerated forward inclination of the trunk reduced towards control values in all therapeutic conditions. There was a tendency for L-dopa to increase trunk movements in the frontal plane, similar to events seen in quiet stance. Due to the presence of additive and synergistic effects, we concluded that the mechanisms of action of the two treatments are likely to be different.