Physical training games so-called exergames might complement traditional physiotherapy to help older adults suffering from Parkinson’s disease to slow the progress and ease symptoms of this nonreversible disease. Adding social aspects, such as multiplayer gaming, could potentially increase the motivation to play and thereby exercise. This paper investigates two design options for cooperative multiplayer exergaming, called strong and loose cooperation. Employing a specifically developed window washer game, a user study with 22 patients with Parkinson’s disease was conducted, indicating that strong cooperation entails benefits such as increasing communication and coordination between the players, resulting in higher overall scores. Nevertheless, 50% of the participants preferred the loose cooperation mode.