Though not every patient has all features, commonly found signs include macrocephaly, congenital macrosomia, extensive cutaneous capillary malformation (naevus flammeus or port-wine stain type birthmark over much of the body; a capillary malformation of the upper lip or philtrum is seen in many patients with this condition), body asymmetry (also called hemihyperplasia or hemihypertrophy), polydactyly or syndactyly of the hands and feet, lax joints, doughy skin, variable developmental delay and other neurologic problems such as seizures and low muscle tone.

Various sets of criteria have been suggested to identify the disorder in an individual patient, all of which include macrocephaly and a number of the following: somatic overgrowth, cutis marmorata, midline facial birthmark, polydactyly/syndactyly, asymmetry (hemihyperplasia or hemihypertrophy), hypotonia at birth, developmental delay, connective tissue defect and frontal bossing.

The distinctive vascular abnormalities of the skin often fade over time, making the diagnosis challenging in older children with this condition.

[10][11] Like other syndromes associated with disproportionate growth, there appears to be a slightly increased risk of certain types of childhood malignancies in M-CM (such as Wilms' tumor).

Some degree of developmental delay is expected in almost all cases of M-CM, so evaluation for early intervention or special education programs is appropriate.

Recently published management guidelines recommend regular abdominal ultrasounds up to age eight to detect Wilms' tumor.

AFP testing to detect liver cancer is not recommended as there have been no reported cases of hepatoblastoma in M-CM patients.

[citation needed] Prognosis varies widely depending on severity of symptoms, degree of intellectual impairment, and associated complications.

[citation needed] This disorder was recognized as a distinct syndrome in 1997 and named macrocephaly-cutis marmorata telangiectasia congenita or M-CMTC.