Neurofeedback (NFB) research has reported improved concentration and attention in children with attention deficit/hyperactivity disorder (ADHD) and progress maintained over time. Would that also apply to children with an IQ between 50 and 70 (mild mental retardation [MMR]) and an IQ between 70 and 85 (borderline retardation [BR]) with characteristics of ADHD? To our knowledge this is the first NFB treatment study with long-term follow-up in this particular group. Ten adolescents with MMR and BR and ADHD received 30 sessions of quantitative electroencephalogram (QEEG)-based NFB. QEEG differences with a gender- and age-matched group without mental handicap and ADHD (data provided by BRAINnet) were investigated, at pre- and posttreatment and at 6-month follow-up. Neuropsychological functioning was tested administering the Bourdon-Vos, and the Amsterdam Neuropsychological Testing Program subscales SA DOTS and SSV. Pretreatment eyes-closed EEGs were not statistically different in the children with MMR compared to the controls. With eyes open higher amplitudes were found in the lower frequencies in the children with MMR, normalizing over time. The neuropsychological tests improved for reaction times and errors. On the complex tasks in the SSV a number of errors remained. The subjects perceived an improvement in ADHD and increasingly enjoyed the study. After NFB treatment, attention and concentration in children with MMR and BR have improved. Task span and effort also increased, although impulse control remained weak. This may be explained by a limited working memory capacity. The subjective reports may have been affected by situational factors and should be interpreted with caution. This study is limited by its nonrandomized design.