Relapse of acute lymphoblastic leukaemia (ALL) occurred in the anterior segment of four children. All cases had been treated according to the Medical Research Council's UK Acute Lymphoblastic Leukaemia trial protocol (UKALL) including 2 years of continuation chemotherapy. In three cases the diagnosis was confirmed by anterior chamber aspirate while in one case the diagnosis was presumed on clinical grounds alone. All four cases experienced isolated leukaemic relapse in the anterior segment within 2 months of stopping therapy. The months immediately following cessation of continuation chemotherapy as part of the UKALL regime appear to represent a 'high-risk' period for primary anterior segment relapse of ALL. Children with ALL presenting with uveitis should be regarded as having leukaemic relapse and anterior chamber taps with or without an iris biopsy should be considered to confirm this diagnosis. Early diagnosis and treatment of ocular leukaemic relapse is likely to give these children the best chance of ultimate cure.