Historically, underserved racial and ethnic populations have been disproportionately affected by delayed diagnosis. In this review of quantitative studies conducted in the US, patients and caregivers in underserved communities reported several factors contributing to delayed diagnosis. Socioeconomic and sociocultural factors included healthcare avoidance, stigma, and distrust in the healthcare system. Health system factors included poor organizational health literacy and provider-related factors such as cognitive biases. There was a lack of research on diagnosis of chronic conditions, and no studies focused on Asian Americans and Pacific Islanders.