The aim of the present study is to investigate the relationship between language comprehension and language production in Swedish children. This was done longitudinally with 10 children with specific language impairment (SLI), aged 4;0 to 6;3 at Time I, and 10 children with unimpaired language development, aged 3;1 to 3;7 at Time I. The target structure was subordination, more precisely relative clauses. The children's comprehension was tested with picture pointing, act-out and oral response tests. Their production was tested with elicited imitation and sentence completion tests. Data were collected twice, with an interval of six months. The results from the unimpaired children at Time I showed a difference between comprehension and production. At Time II these children scored higher on production than on comprehension. The children with SLI scored significantly higher on comprehension than on production at Time I. In half of the SLI group there was a clear development between the two data collection sessions, diminishing the dissociation. On neither testing did the children with SLI differ significantly from the unimpaired children in comprehension. At both testings, however, the children with SLI had significantly more responses where they did not insert the complementizer in relative clauses. The results indicate that the relationship between comprehension and production is different at different stages in development. They also show that structures involving dependency relations are particularly difficult to produce for children with SLI.