Abstract Objectives Although children with medical complexity (CMC) with high health resource utilization use outpatient structured clinical programs (SCP) to optimize their health, little is known about variation in trends of their health service use shortly after enrollment. We measured these trends and assessed the utility of patient characteristics to predict them. Methods Retrospective analysis of 506 CMC newly enrolled in an outpatient, academic SCP. We measured outpatient and inpatient health service use for the first 6 months following enrollment. Using cluster analysis, we categorized CMC with similar trends by health service. We assessed patient demographic (e.g., age) and clinical [type and number of complex chronic conditions (CCC)] characteristics with the cluster categories. Results Most (90.3%) CMC enrolled had ≥1 CCCs; 53.8% had ≥3 CCCs. For all CMC, outpatient specialty visits, phone calls, and hospitalizations (not involving ICU) decreased significantly over the first 6 months after enrollment. For example, the hospitalization rate decreased from 9.7% to 4.5% in the 1st and 6th months, respectively, (P < 0.001). Cluster analysis revealed four categories of hospitalization trends, 6 months after enrollment: 72.9% of CMC had no hospital use; 16.0% had increased then decreased use; 8.3% had decreased use; and 2.8% had increased use. No patient and clinical characteristics clearly distinguished which hospitalization trend CMC experienced. Conclusions Although the overall population of CMC experienced decreased outpatient and inpatient health services utilization over time, this decrease was not uniformly experienced. Fundamental patient demographic and clinical characteristics did not predict health service trends.