In a study of special education programs in five urban school systems, parent interview data for 1726 children revealed how early the children's problems were identified and how the medical system was involved in the diagnosis. Problems included speech impairment, learning disabilities, emotional disturbance, mental retardation, sensory disorders, and physical and health disabilities. Overall, 4.5% of the children's problems were identified at birth, and only 28.7% before the age of 5 years. Variation in age at identification depended on the condition: 1 year for Down syndrome and cerebral palsy versus a 6-year range for mental retardation. Although physicians were most likely to identify the less common, more severe handicaps, they also identified from 15% to 25% of learning disabilities, speech impairments, emotional disorders, hyperactivity, and "other" development problems. The type, severity, and complexity of the condition were significant predictors of physician identification. No racial, socioeconomic, or site biases were associated with whether a physician was first to identify. Age at identification was predicted by the complexity of the problem, the association with other health and developmental concerns, socioeconomic indicators, and whether a physician was involved in the diagnosis. In the absence of clear assumption of responsibility for early identification, much terrain remains uncharted by medical practitioners and the schools. A better systematic sharing of responsibility for the early identification of developmentally disabling conditions is needed.