Retinoblastoma is the most frequently occurring primary intraocular malignant tumour in children (12-15 new patients per year in the Netherlands). It occurs in one or two eyes. Bilateral retinoblastoma, which occurs in 40% of the cases, is always hereditary; unilateral retinoblastoma, which is found in 60% of cases, is hereditary in 10% of these cases. The presenting symptoms are: leucocoria, strabismus or a red, painful eye. Early detection of retinoblastoma is important for the chance of survival, the visual prognosis and preservation of the eye. The choice of treatment is based on the risk of metastases, the diameter and the location of the tumour, the age of the patient, the heredity and the visual prognosis. Nowadays, treatment more often consists of a combination of techniques. Enucleation is carried out when a large tumour fills over half of the globe; often this is the only possible treatment. Small tumours (diameter and thickness < 2 mm) in the centre of the retina can be treated with laser therapy and those in the peripheral retina by cryotherapy. Small to medium-sized tumours (< 8 mm diameter) can be treated with thermochemotherapy: systemic chemotherapy and laser hyperthermia, if necessary with adjuvant laser therapy or brachytherapy. Medium-sized tumours (< 8 mm thick) can be treated with just brachytherapy, sometimes preceded by chemoreduction.