In Sheko, an Omotic language spoken in Ethiopia, verb forms in adverbial clauses employ a number of poorly-understood morphemes which are not found in the verb forms of main clauses. So far adverbial clauses in Sheko have received little treatment; only Aklilu (1988:90-91) gives some useful information. However, this topic is of general interest, in view of the fact that adverbial clauses are in between complement clauses and relative clauses (Payne 1997:307). A comparison of the different clause types raises some pertinent issues in the syntax and verb morphology of Sheko, such as the formal relationship between some morphemes in adverbial clause marking on the one hand and case markers and the relative clause marker on the other hand.