Moonlight Syndrome is an adventure game developed and published by Human Entertainment for the PlayStation in October 1997. A spin-off of the company's Twilight Syndrome series, the game was directed and co-written by Goichi Suda. Retaining the combination of adventure and visual novel elements from earlier games in the series, Moonlight Syndrome follows series protagonist Mika Kishii as she is reluctantly pulled into investigating supernatural phenomena.
Development of Moonlight Syndrome began following the completion of Suda's work on the first Twilight Syndrome games. Due to having little input on the original games' stories and disliking the ghost story elements, Suda focused the plot of Moonlight Syndrome around psychological horror and human capacity for evil. The game received average reviews upon release, and influenced both Suda's later work and the scenario writer of Siren. Following the release of Moonlight Syndrome, Suda left Human Entertainment to form Grasshopper Manufacture.