The medical/research records of 1014 patients diagnosed at the Washington State Fetal Alcohol Syndrome (FAS) Diagnostic and Prevention Network (DPN) of clinics were used to develop a new, comprehensive, reproducible method for diagnosing the full spectrum of outcomes among patients with prenatal alcohol exposure. This new diagnostic method, called the 4-Digit Diagnostic Code, was compared to the standard gestalt method of diagnosis on the first 454 patients who had received a gestalt diagnosis of FAS, atypical FAS (AFAS) or possible fetal alcohol effect (PFAE) prior to the development of the 4-Digit Diagnostic Code. The outcomes of the patients were more accurately and comprehensively documented by the 4-Digit Diagnostic Code, because of its use of quantitative, objective measurement scales and specific case definitions. The four digits in the code reflect the magnitude of expression of the four key diagnostic features of FAS in the following order: (1) growth deficiency; (2) the FAS facial phenotype; (3) central nervous system damage/dysfunction; (4) gestational alcohol exposure. The magnitude of expression of each feature is ranked independently on a four-point Likert scale with 1 reflecting complete absence of the FAS feature and 4 reflecting a strong 'classic' presence of the FAS feature. The 4-Digit Diagnostic Code is being used effectively for diagnosis, screening, and surveillance efforts in all Washington State FAS DPN clinics.