In this paper the results of a meta-analysis of the effectiveness of psychological treatment for relationship problems in children and adolescents are presented. A total of 15 articles, which fulfilled the selection criteria, were identified leading to 24 independent studies. They were used to work out the standardized mean difference between the treated group mean minus the control group mean. The mean effect size at the pos-test (d+= 0.59) and follow-up (d+= 0.64) showed the effectiveness of the treatment for decreasing and eliminating shyness and social phobia, as well as the symptoms of maladjustment, improving self-esteem and social skills. All in all, significant differences were found among the different treatment components, and the combination of exposure, social skills and cognitive techniques proved to be the best method. Other outstanding variables were the duration, frequency and intensity of the treatment, age and gender of the samples, mortality and experimental quality. Finally, the results are discussed and several suggestions are made to help in future research into these behavioral problems.