Diagnostic criteria for Prader-Willi syndrome (PWS), developed by consensus of seven clinicians in consultation with experts, are reported from the University of Washington, Seattle, and six additional centers. Three categories evolved, scored on a weighted point system: 1) Major criteria (1 point) include neonatal hypotonia, feeding problems, excessive weight gain, characteristic narrow facies with almond-shaped eyes and small, down-turned corners of the mouth, hypogonadism, developmental delay with mild to moderate mental retardation or learning problems, hyperphagia and obsession with food, and chromosomal deletion 5q11-13. 2) Minor criteria (one half point) include weak cry, behavioral problems, sleep apnea, short stature, fair skin and hair, small hands and feet, myopia, viscous saliva, and speech defects. 3)Supportive criteria (unscored) include high pain threshold, temperature instability, scoliosis, osteoporosis, and expert at jigsaw puzzles. Symptoms change with age: 5 points (4 major) required for diagnosis at birth to 3 years; 8 points (5 major) in the 3 year to adult age groups. 
COMMENT. Until a biological marker for PWS is available, the diagnosis is more an art than a science. These clinical criteria should ensure uniformity and alert the physician to a suspicion of PWS in hypotonic infants and in obese, mildly retarded and behaviorally disturbed adolescents and adults.