Abstract This study investigates children’s vocabulary knowledge in Finnish Sign Language (FinSL), specifically their understanding of different form-meaning mappings by using a multilayered assessment format originally developed for British Sign Language (BSL). The web-based BSL vocabulary test by Mann (2009) was adapted for FinSL following the steps outlined by Mann, Roy and Morgan (2016) and piloted with a small group of deaf and hearing native signers (N = 24). Findings showed a hierarchy of difficulty between the tasks, which is concordant with results reported previously for BSL and American Sign Language (ASL). Additionally, the reported psychometric properties of the FinSL vocabulary test strengthen previous claims made for BSL and ASL that the underlying construct is appropriate for use with signed languages. Results also add new insights into the adaptation process of tests from one signed language to another and show this process to be a reliable and valid way to develop assessment tools in lesser-researched signed languages such as FinSL.