Background: German participles are formed by a co-occurrence of prefixation and suffixation. While the acquisition of regular and irregular suffixation has been investigated exhaustively, it is still unclear how German children master the prosodically determined prefixation rule (prefix "ge-"). Findings reported in the literature are inconsistent on this point. In particular, it is unclear whether participle formation is vulnerable in German children with specific language impairment (SLI). Aims: To compare children with and without SLI in their abilities to form German participles correctly, and to determine their relative sensitivities to the morphophonological regularities of prefixation. Methods & Procedures: The performance of 14 German-speaking children with SLI (mean age = 7;5) in a participle formation task was compared with that of age-matched and younger typically developing controls. The materials included 60 regular verbs and 20 pseudo-verbs, half of them requiring the prefix "ge-." Outcome & Results: Overall, children with SLI performed poorly compared with both groups of typically developing children. Children with SLI tended either to avoid participle markings or choose inappropriate affixes. However, while such children showed marked impairment at the morphological level, they were generally successful in applying the morphoprosodic rules governing prefixation. Conclusions & Implications: In contrast to earlier findings, the present results demonstrate that regular participle formation is problematic for German children with SLI.