Background The Box and Block Test (BBT) is a highly recommended outcome measure to assess unilateral gross motor activity of the upper limbs. The BBT has not previously been available in a version adapted to the Spanish context. Thus, this study aimed to cross-culturally adapt and translate the BBT’s instructions and pilot test the Spanish version of BBT in adults with acquired brain injury (ABI). Methods The BBT was translated and cross-culturally adapted following standard procedures. An expert committee approved the final Spanish version of BBT and it was conceptually validated by four therapists with expertise in ABI. The tool was tested on 14 adults with ABI. Results The Spanish version of BBT included a new section of materials for the test and a record to count the number of blocks transferred from one compartment of the box to the other. Following the pilot study, a modification in terminology was implemented for referring to the dominant and non-dominant hands. Conclusions Our results suggest that the Spanish version of BBT is suitable for assessing manual dexterity in Spanish-speaking adults with ABI.