Excessive synchronization of the basal ganglia neuronal activity in the 13- to 35-Hz frequency band, so-called beta activity, has been associated with the motor deficits of Parkinson's disease (PD). Studies have demonstrated that beta activity may be suppressed by treatment with dopaminergic medication and high-frequency stimulation of the subthalamic nucleus (STN), with the degree of suppression correlating with clinical improvement. However, these studies failed to demonstrate any correlation between beta activity of parkinsonism in the resting, untreated state. This argues against a significant relationship between beta activity and motor impairment. Here we use an advanced nonlinear dynamical analysis method based on the Lempel-Ziv estimator to show frequency band and symptom–subset specific correlations between STN local field potential (LFP) complexity and motor impairment in PD patients. Oscillatory activity has a reduced complexity, and we found a strong negative correlation between the complexity of the STN LFP over the 13- to 35-Hz frequency range and akinesia–rigidity. There was no such correlation with tremor. Furthermore, there was no correlation between LFP Lempel-Ziv complexity (LZC) over the 0- to 12-Hz frequency band and any parkinsonian motor impairment. The results strengthen the association between the dynamic structure of synchonised (LFP) activity in the beta frequency band in the STN and akinesia–rigidity.