Children with this condition may be small at birth, with increased hair on the body and face, and with poorly developed fingernails and toenails. They may also have poor muscle tone. Facial features that may be present with this syndrome include a flat bridge of the nose; an underdeveloped vertical groove in the center of the upper lip (philtrum); a large mouth; and malformed ears. Features specific to the eyes may include down-slanted eyes; widely spaced eyes (hypertelorism); crossed eyes (strabismus); drooping eyelids (ptosis); and/or epicanthal folds (skin folds of the eyelid covering the inner corner of the eye). Other features that have been reported include a short or webbed neck and low-set hair line. Growth deficiencies may include underdeveloped fingers and/or toes, malformed nails, as well as finger-like thumbs.

These features are often associated with growth delay and varying degrees of developmental delay. The risk for an affected child to be neurologically impaired is estimated at 1 to 11 % (two to three times higher than for the general population). The risk of cleft lip and/or palate and heart defects is estimated to be about five times higher among exposed infants. Some case reports have suggested an increased risk for the occurrence of benign (noncancerous) or malignant (cancerous) tumors, such as neuroblastoma or other neonatal tumors (ependymoma, ectodermal tumors, Wilms tumor).

As children with fetal hydantoin syndrome grow older, the developmental delays typically improve but studies suggest that they may remain slightly behind siblings that have not been exposed. The growth delays remain through life, as does the tendency to have increased body hair (hirsutism).