Autism Spectrum Disorder (ASD) has undergone significant diagnostic evolution, culminating in DSM-5’s unification of previously distinct conditions such as autism, Asperger’s disorder, childhood disintegrative disorder, and PDD-NOS—a move that simplified labels but obscured crucial differences. The historical trajectory reveals both scientific progress and persistent misunderstandings, while DSM-5’s framework introduces ambiguities, challenges in adult diagnosis, and cultural and gender biases. Screening and assessment tools, though valuable, remain limited by accessibility, age focus, and cultural relevance, particularly in diverse populations. Recognizing adults with autism is critical to preventing mental health crises and promoting functional inclusion. A refined classification model, distinguishing high- and low-functioning autism with subtypes and severity levels, restores nuance, enhances diagnostic precision, supports tailored interventions, and affirms the dignity of autistic individuals. By integrating clinical, research, policy, and lived perspectives, a more humane, evidence-based approach emerges that emphasizes inclusion, individualized care, and the recognition of neurodiverse potential.