Lateral trunk flexion is often seen in patients with Parkinson disease, sometimes coming on as a subacute phenomenon associated with medication adjustments, and in others with gradual onset that seems related to a neurodegenerative process related to the evolution of the disease.Either acute or subacute presentations seem to be pure abnormalities in the coronal plane and are usually reversible. However, a chronic form occurs often in a combined fashion with anteroposterior flexion (camptocormia), improves only partially, remains stable, or even worsens over time.The acute/subacute phenotype is the condition originally named as Pisa syndrome (PS).The pathophysiology of PS remains poorly understood, and a cholinergic-dopaminergic imbalance has been suggested as being involved in the cause of this disorder. The role of other neurotransmitters and how they become dysfunctional in PS remains to be elucidated.Specific treatments, other than discontinuing the medications responsible for the disorder, whenever possible, are undeveloped because of the unknown etiology.