Introduction: Parkinson's Disease (PD) may lead to cognitive symptoms, including visuo-spatial attentional deficits such as unilateral spatial neglect (USN). Although there is some evidence for USN in PD patients, especially in those with left-sided onset of motor-symptoms (LPD), previous studies revealed inconsistent and highly variable results in neglect tasks using line bisection and have not systematically compared LPD with RPD (PD patients with right-sided onset) or healthy controls (HC). Methods: We designed a fully automatized online web-based line bisection task and tested a group of 170 PD patients (81 RPD, 66 LPD) and 45 HC. Results: Our data reveals (1) a rightward bias on line bisection in LPD compared to HC and RPD, (2) right-sided pseudoneglect in HC as well as RPD. Our data also reveals that (3) PD patients, independent of the primarily affected side, are more variable in their line bisections. Conclusion: These data provide robust evidence for systematic changes in visuo-spatial perception in PD and present a new online diagnosis and monitoring tool for USN to evaluate patients at their home.