An English to Spanish translation procedure and its associated dictionaries were developed and implemented for the 1,426 terms of the morphology section of the International Classification of Diseases for Oncology. Morphological substitutions and respefling rules permit translation of most of the ICD—O vocabulary composed of Latin and Greek derived terms, which are cognate in the source and target languages, without the construction of a large word lexicon.A fairly simple classification of words which could be implemented by recognition of terminal morphemes, and which classifies them both syntactically and semantically served as an adequate basis for translation, and sheds some light on the linguistic structure of this type of complex noun phrase seen universally in medical writings and communications. A set of 17 reduction-transformation rules based on the word classification provide syntactic control of the translation process.