A baby born with Down syndrome is diagnosed based on physical examination. Typical characteristics are low muscle tone and loose joints, a flat facial profile and an upward slant to the eyes. The ears are usually small and there is a single crease across the palms instead of the double crease normally seen. Down babies is usually of normal birth size but tend to grow at slower rates than other babies. Their low muscle tone usually leads to sucking problems, constipation and other digestive problems.

Developmental milestones are usually delayed such as speech, self-care, feeding and toilet training.