Parkinsonian handwriting is typically characterized by micrographia, jagged line contour, and unusual fluctuations in pen velocity. In this paper we present a computational model of handwriting generation that highlights the role of the basal ganglia, particularly the indirect pathway. Whereas reduced dopamine levels resulted in reduced letter size, transition of STN–GPe dynamics from desynchronized (normal) to synchronized (PD) condition resulted in increased fluctuations in velocity in the model. We also present handwriting data from PD patients (n = 34) who are at various stages of disease and had taken medication various lengths of time before the handwriting sessions. The patient data are compared with those of age-matched controls. PD handwriting statistically exhibited smaller size and larger velocity fluctuation compared to normal handwriting.