We report the first case of T-cell gamma delta+ hepatosplenic malignant lymphoma in childhood. Tumour-specific oligoprobes were developed against the single V1-J1 rearrangement of the delta T-cell receptor (TCR) gene in order to perform minimal residual disease (MRD) studies. Molecular analysis in serial bone marrow samples proved to be of predictive value concerning the clinical outcome. Clonotypic DNA was not detected in peripheral blood during the course of the disease until a refractory terminal leukaemic phase took place 18 months after the diagnosis. This case demonstrates the usefulness of MRD studies to monitor the course of disease in at least some subsets of peripheral T-cell lymphomas.