Advances in newborn screening, molecular diagnostics, and targeted therapies have markedly improved survival for individuals with inborn errors of metabolism (IEM), allowing many to live well into adulthood. While some may remain asymptomatic, their underlying metabolic vulnerabilities persist and can be unmasked by illness, stress, or other triggers. As a result, a growing population of adults with IEM now faces unique and evolving challenges related to long-term disease management, continuity of care, and quality of life. Despite these shifting demographics, there remains limited literature directly comparing pediatric and adult treatment outcomes, and emerging data suggest that therapeutic effectiveness in childhood may not always extend into adulthood. Survivorship in IEM spans a wide range of medical, neurodevelopmental, and psychosocial domains. These include maintaining metabolic stability, managing complex dietary needs, monitoring for progressive organ dysfunction, addressing neurocognitive outcomes, and navigating socioeconomic and mental health challenges. Compounding these issues are barriers such as limited access to specialized adult care, inconsistent insurance coverage for medical foods and therapies, and a lack of established adult-specific treatment protocols. This review explores the critical components of survivorship in IEM, including emerging therapies and the increasing importance of multidisciplinary care models. It underscores the necessity of well-coordinated transition programs that support adolescents and young adults as they shift from pediatric to adult healthcare systems. In addition, it highlights the need for expanded education and research efforts aimed at understanding and addressing the distinct and evolving needs of adults with IEM. By highlighting the lived experience, gaps in education, and complex care requirements of this growing patient population, this invited manuscript aims to inform tailored, lifespan-focused management strategies that reflect the realities of aging with a rare metabolic disorder.