The objectives of this study were 1) comparing the magnitude of the deficit in social skills of adolescents in the sample as compared to those reported in other studies, and 2) providing evidence on which effects generated by the programme for “Intervention for adolescents with social phobia” (IASP) can be attributed to the component of social skills training (SST). Accordingly, we designed an investigation with a treatment group in which the entire program applies IASP (G1) and another group (G2) in which the SST component was removed. The sample consisted of 41 Spanish adolescents with a mean age of 14.95 years (SD: 1.3, range: 14-18), with a majority of girls (63.41%). All met the criteria required for the diagnosis of Generalized Social Phobia (GSP). The results show that: (i) The subjects in our sample show deficits in social skills similar to those found for the population with GSP magnitudes; (ii) Statistically significant differences between groups in favor of G1 were found. The intra-group effect sizes were much higher in the group with SST. The role of SST is very relevant.