Young adults with childhood-onset rheumatic diseases are more frequently establishing and continuing care with adult rheumatologists. The transfer of care can be challenging for both the young adult patients and their adult rheumatologists, in large part due to differences between pediatric-onset rheumatic diseases and their adult-onset counterparts, or due to the rarity of some pediatric-onset rheumatic conditions. Other challenges are due to cultural differences between pediatric and adult medical care and to the young adult needing to increasingly perform self-management skills that were previously managed by parents or other caregivers. In this review, we will provide a summary of strategies for working effectively with young adults as they transition to adult care. We will then discuss a subset of childhood-onset rheumatic diseases—including juvenile idiopathic arthritis, localized scleroderma, autoinflammatory diseases, pediatric-onset systemic lupus erythematosus, juvenile-onset dermatomyositis, and autoimmune encephalitis—for which clinical manifestations, management, and prognosis frequently differ between pediatric onset and adult onset. Our aim is to highlight differences that make caring for this population of transitioning young adults unique, providing tools and knowledge to empower the adult rheumatologist to care for these young adults in ways that are evidence-based, effective, efficient, and rewarding.