Common traits include borderline to mild intellectual disability, infertility, radioulnar synostosis (the fusion of the long bones in the forearm), and in some cases tall stature.

[1] A number of minor skeletal anomalies are observed, such as clinodactyly,[5] radioulnar synostosis (the fusion of the long bones in the forearm), and poor dental development.

[2] As very few cases of XYYY syndrome in adult men have been reported, drawing certain conclusions about sexual functioning and reproduction is difficult.

[2][6] Two men with XYYY syndrome are known to have had independent adult lives, marrying and finding employment, and only came to medical attention for infertility.

Some patients have been transferred to special schools, high-security group homes, or institutions due to severe aggression.

[1] Though teenage boys with XYYY syndrome may be at-risk adolescents, they are capable of positive identity formation, and case reports following the identity formation and personal development of XYYY adolescents have demonstrated a desire to have healthy relationships and integrate successfully into society.

[20] XYY syndrome is known to have a milder phenotype in cases found by chance, such as during prenatal screening, than in those karyotyped due to a medical or behavioural indication.

[1] The two syndromes have a number of symptoms in common, such as tall stature (although the height increase in XYY appears greater than that in XYYY[1][18]) and behavioural issues.

One significant observed distinction is that while males with 47,XYY karyotypes usually have normal fertility, 48,XYYY appears associated with infertility or sterility.