We describe a 38-year-old woman who developed symptoms of hallucinogen persisting perception disorder (HPPD) after using lysergic acid diethylamide (LSD) once and continued to have symptoms of HPPD for nearly 17 years, although she did not use LSD after her first use. The symptoms of HPPD were temporally related to her first LSD use and she responded well to risperidone within a few weeks of...