We report clinical findings in 17 adults with Costello syndrome ranging in age 
from 16 to 40 years. Two patients in this series have had bladder carcinoma, the 
only malignancy reported to affect adults with Costello syndrome. Benign tumors 
included multiple ductal papillomata in two women, and a fourth ventricle mass 
in one man, thought to be a choroid plexus papilloma. Endocrine problems in this 
series were osteoporosis, central hypogonadism, and delayed puberty. Other 
health problems were symptomatic Chiari malformations in three patients. Four 
patients had adult-onset gastro-esophageal reflux, three of whom had Chiari 
malformations. Fourteen adults had mild to moderate intellectual disability with 
three individuals having severe intellectual disability; 15 individuals attained 
some reading and writing skills and 14 showed ongoing acquisition of new skills 
into adulthood. On the basis of this data, we recommend that neuro-imaging be 
considered in adults with Costello syndrome if they develop symptoms suggestive 
of a Chiari malformation. In the event of pubertal delay, endocrine 
investigations are indicated and hormone treatment may be required. Bone density 
assessments should be performed in adults with Costello syndrome, particularly 
in those with pubertal abnormalities. Screening for microscopic hematuria as a 
marker for bladder carcinoma may be indicated, although this requires further 
evaluation.