Chemotherapeutic or radiotherapeutic regimens are being increasingly used in low grade glioma of childhood. These protocols require methods to monitor tumor activity. We report our experience in eleven patients. The tumors were localized in the optic pathway (3), cerebral cortex (4) and thalamus/hypothalamus (4). Histological diagnoses included low grade astrocytoma (6), gliofibroma (1) and ganglioglioma (2). Two children with neurofibromatosis type 1 (NF-1) and typical optical tumors were not biopsied. 13 episodes of progression were noted including 3 altered diagnoses. This was evident from clinical symptoms in 11/13 episodes, computed tomography (CT) or magnetic resonance imaging (MRI) in 10/13 situations, iodine-123-alpha-methyltyrosine (123I-IMT) single-photon emission computed tomography (SPECT) in 10/10 situations, fluorine-18 fluorodesoxyglucose (18F-FDG) positron emission tomography (PET) in 0/3 and thallium-201 (201Tl) SPECT in 1/1. Seven responses to chemotherapy were recorded. Clinical symptoms indicated this in 7/7 situations, MRI in 5/7, 123I-IMT SPECT in 1/2 and 201Tl SPECT in 1/1. These data suggest that 123I-IMT SPECT is a valuable addition to low grade glioma diagnostic and stress the need for a prospective study.