OBJECTIVE To determine the audiological and clinical results of cochlear implantation in children below the age of 12 years old with congenital and acquired single-sided deafness. DESIGN Observational, descriptive, transversal study. MAIN OUTCOME MEASURES Speech reception thresholds, Cortical responses, Auditory Lateralization Test and SSQ questionnaire. PARTICIPANTS Children < 12 implanted for congenital or acquired SSD. RESULTS All the children with congenital SSD showed positive cortical responses. Positive results were obtained in the Auditory Lateralization Test for the following modalities: 0o, 45o and 90o. With respect to the Speech Test, the children with acquired SSD showed the following results: 92% and 100% in recognition and 48% and 68% (Azimuth modalities), Signal CI side 52% and 68% and Signal normal hearing side 44% - 60% (p < 0.05). In both group the processor was used for 6-12 hours. With respect to the SSQ questionnaire results, the parents were more satisfied within the post-operative period than within the pre-operative period (P