Purpose: The authors' primary goal was to investigate the potential of past tense inflection as a clinical marker of Danish specific language impairment (SLI). They also wished to test the predictions of the extended optional infinitive (EOI) account and processing based accounts of SLI on Danish. Method: Using sentence completion and sentence repetition tasks, the authors investigated the use of past tense by 3 groups (n = 11 in each group): (a) children with SLI whose ages ranged from 5;2 (years;months) to 7;11; (b) children with typical language development matched on chronological age; and (c) children with typical language development matched on vocabulary. Results: Participants with SLI were less likely to produce past tense than were both typically developing control groups. In particular, only the children with SLI had difficulties with accurately producing past tense verbs during the sentence repetition task. Past tense accuracy was associated with children's productive vocabulary levels and proficiency with a nonword repetition task. Conclusion: Past tense use is potentially a clinical marker of Danish SLI, but more research is needed to confirm this. Results provided mixed support for competing accounts of SLI.