OBJECTIVES: In short term clinical trials antipsychotic medications are well tolerated by children under six years old. While concerns have been raised about the impact of long term exposure on metabolic and cardiovascular health and on the developing brain, little is known about the extent of long term antipsychotic exposure in this age group. This study quantifies antipsychotic exposure over a 4 year period of children who began antipsychotic treatment before their sixth birthday and identifies the variables associated with the risk of long term exposure. METHODS: Children were identified who initiated an index episode of antipsychotic treatment before their sixth birthday in Florida’s fee for service Medicaid program. Using claims data the medication utilization of these children was tracked during the year before and the four years following the start of their index episodes (pre-index and four post-index periods). Generalized estimating equations were used to identify variables associated with the risk of additional days of antipsychotic exposure. RESULTS: Five hundred twenty-eight children were included in the cohort. The mean total days of exposure was 821.9 (±431.9) representing 56.3 % of all days during the four post-index periods. The mean days of exposure to combinations of antipsychotics and other classes of psychotherapeutic medications were 623.8 ±447.6 days. Children with primary diagnoses of pervasive developmental disorders and affective disorders were at greater risk of additional days of exposure than children with ADHD. Exposure tended to be greater among children with indicators of clinical complexity including the presence of secondary diagnoses and the use of other classes of psychotherapeutic medications in addition to antipsychotics. CONCLUSIONS: Exposure to antipsychotic mediations was extensive. Although these children may have had complex and severe problems, additional research is urgently needed on the benefits and risks of long term antipsychotic exposure among very young children.