To date, there are 12 reported cases of hepatoblastoma in trisomy 18 patients, three of whom had a mosaic chromosome pattern. We report on an 18-month-old child who had hemihypertrophy and developmental delay, was found to have hepatoblastoma on surveillance ultrasound scan, and was subsequently diagnosed with mosaic trisomy 18 on array comparative genomic hybridisation from a peripheral blood sample and molecular cytogenetic analysis of the tumour specimen. Although hemihypertrophy has been associated with mosaic trisomies, there are only a couple of published case reports of hemihypertrophy or asymmetry in mosaic trisomy 18 patients and none in the reported cases of hepatoblastoma in a mosaic trisomy 18 setting. We have reviewed the published case reports of hepatoblastoma in trisomy 18 patients and found that they seem to tolerate the intensive treatment very well if there are no significant comorbidities.