The medical literature has followed educational outcomes of Medicine-Pediatric (Med/Peds) physicians, but limited studies exist as to clinical outcomes for these combined specialty physicians. Although a variety of practice environments are available for a growing number of Med/Peds physicians, a collaborative practice setting with family physicians may optimize the Med/Peds practice potential. This study investigates clinical practice outcomes and utilization efficiencies of collaborative Med/Peds family practice physicians within a community, which should provide an effective model in a growing managed care environment. Two collaborative practice settings in a moderate size Midwest community were analyzed with respect to patient demographics and utilization scores provided by a practice management group and a nationally based health care network. Current Procedural Terminology (CPT) coding was used to follow demographic trends for over 45,000 patient visits for 1 year. Efficiency ratings (Z-scores) were used over the same year for over 6,000 health care network patient visits to 10 collaborative practice-based physicians, which were then compared to 141,101 community family practice patient encounters, 26,617 general internist patient encounters, and 29,995 patient encounters to pediatricians for utilization trends. Med/Peds and Family Practice patient care data reflected nearly identical patient demographics between specialties with only a few exceptions. Med/Peds physicians cared for three times the total number of children less than 2 years old. Med/Peds physicians experienced a higher complexity of illness, in part due to a 40% increase in internal referrals from family practice colleagues in the ambulatory care setting, while maintaining a third of the proportion of outpatient referrals. Cost-effective interoffice utilization was still maintained, supported by a more optimal efficiency rating for Med/Peds physicians compared to collaborative family practice colleagues. Inpatient efficiency was demonstrated for Med/Peds specialists even though a threefold increase in hospitalizations was observed, in part resulting from physicians within these collaborative practices arranging all newborn nursery and pediatric admissions be covered by Med/Peds physicians. Both collaborative primary care specialists demonstrated more cost-effective overall practice utilization scores when compared to community-based primary care specialists. Med/Peds physicians in this study have been trained to provide cost-effective patient care in both outpatient and inpatient settings. Decreased outside referrals by collaborative family practice physicians through utilization of Med/Peds colleagues serves to optimize practice economy by eliminating the threat of competition that exists among community-based generalists. Such a model helps to control an overused referral system to subspecialists.