Methods for screening or diagnosing subjects for disorders involving accumulation of one or more oxysterols such as cytotoxic oxysterol accumulation, Niemann-Pick C(NPC) disease, lysosomal storage diseases, cholesterol trafficking diseases, and neurodegenerative diseases. Also provided are methods for methods for screening or diagnosing subjects (including infants and neonatal subjects) for NPC disease, methods for monitoring the progression, remission, and clinical status of NPC disease, and methods for evaluating the efficacy of therapeutic treatment of NPC disease.