This paper presents a finite-state computational model for Spanish Sign Language nominal morphology with particular attention to the tratment of morphological alternations. A computational morphology consists of a lexicon, a rewrite rules component relating lexical representations to surface forms, and a morphotactic component. All these components are compiled into finite-state transducers. Nominal morphology in Spanish Sign Language deals with bound morphemes through inflection, introflection and suppletion. The model and its implementation deal with plurals, numeral incorporation and irregularity and can be extended to other word classes as well to other sign languages. The implemented technology allows the application of the morphology either to the analysis or to the generation of signs.