The quality of interpretations produced by sign language interpreters was investigated. Twenty-five experienced interpreters were instructed to interpret narratives from (a) spoken Dutch to Sign Language of the Netherlands (SLN), (b) spoken Dutch to Sign Supported Dutch (SSD), and (c) SLN to spoken Dutch. The quality of the interpreted narratives was assessed by 5 certified sign language interpreters who did not participate in the study. Two measures were used to assess interpreting quality: the propositional accuracy of the interpreters' interpretations and a subjective quality measure. The results showed that the interpreted narratives in the SLN-to-Dutch interpreting direction were of lower quality (on both measures) than the interpreted narratives in the Dutch-to-SLN and Dutch-to-SSD directions. Furthermore, interpreters who had begun acquiring SLN when they entered the interpreter training program performed as well in all 3 interpreting directions as interpreters who had acquired SLN from birth. (Contains 1 note and 3 tables.)