Background and Objectives: Board certification is acknowledged as the mainstay for ensuring quality physician-delivered health care within medical specialties. The American College of Osteopathic Family Physicians (ACOFP) administers the American Osteopathic Board of Family Physicians' (AOBFP) In-Service Examination (ISE) to provide residents and program directors with a formative examination to assess competency and preparation for successful completion of the AOBFP certifying examination (CE). Unique assessment processes are integral to monitoring development of the osteopathic family physician throughout training and into practice, and to verify their competency for the safety and protection of the public. This study sought to investigate whether performance on the AOBFP ISE predicted performance on the AOBFP CE, and thereby successfully equipped residents to safely enter medical practice., Methods: In 2020, data from 1,893 PGY-1 through PGY-3 residents (2016-2018), whose ISE scores could be matched with scores on the AOBFP initial board CE, were analyzed for this study., Results: Correlations among ISE administrations across 3 years of postgraduate medical education were in the mid-to-high .6 range; the ISE scores correlated with CE scores in the mid .4 to high .5 range. Less reliable measures of positive predictive value were 0.99, and sensitivity was 0.91., Conclusions: Results suggest that ISE administrations during residency training are effective in developing remediation strategies for subsequent successful CE performance. The inclusion of osteopathic principles in the AOBFP CE necessitates inclusion of osteopathic content in resident training exams like ISE.