Research into lexical processes shows that frequency and phonological similarity (neighborhood density) affect word processing and retrieval. Previous studies on inflectional morphology have examined the influence of frequency of occurrence in speech production on the inflectional verb paradigm in English. Limited work has been done to examine the influence of phonological similarity in languages with a more complex morphological system than English. The present study examined the influence of neighborhood density on the processing of Spanish Preterite regular and irregular verbs as produced by thirty native speakers of Spanish. The results of a naming task showed that regular verbs were processed faster and more accurately than irregular ones. Similar to what has been observed in English, a facilitative effect of neighborhood density for -ir verbs was observed in both regular and irregular verbs, such that -ir verbs with dense neighborhoods were produced faster and more accurately than -ir verbs with sparse neighborhoods. However, no neighborhood density effects were observed for -ar verbs (regular and irregular) in reaction times and accuracy rates. Thus, the activation of a specific -ir verb was facilitated by similar sounding verbs regardless of being regular and irregular. Implications for models of morphology language processing are discussed. Keywords: neighborhood density, language processing, Spanish. De acuerdo a investigacion llevada a cabo en torno a procesos lexicos, la frecuencia y la similitud fonologica (vecindario de densidad) afectan al acceso y procesamiento de palabras. Estudios previos sobre morfologia flexiva han examinado la influencia de la frecuencia de aparicion en actos de produccion de habla en el paradigma verbal flexivo del ingles. No existen muchos estudios que examinen la influencia de la similitud fonologica en lenguas con un sistema morfologico mas complejo que el que presenta el ingles. En este estudio se ha examinado la influencia de la densidad de vecindario en el procesamiento de verbos regulares e irregulares del espanol en formas de preterito por parte de treinta nativo hablantes del espanol. Los resultados en una tarea de naming mostraron que los verbos regulares se procesaron mas rapida y correctamente que los irregulares. Al igual que se ha observado en el ingles, se ha encontrado un efecto facilitador de densidad de vecindario en el caso de los verbos -ir, tanto en sus formas regulares como irregulares, de tal forma que los verbos -ir pertenecientes a un vecindario denso se produjeron mas rapida y correctamente que los verbos - ir en vecindarios ermitanos. No obstante, no se han observado efectos de vecindario lexico en los verbos -ar (regulares e irregulares) en cuanto a tiempos de reaccion e indices de precision. Asi pues, verbos similares en pronunciacion facilitaron la activacion de un verbo -ir especifico independientemente si el verbo era regular o irregular. Se plantean implicaciones en los modelos de procesamiento morfologico. Palabras clave: densidad de vecindario, procesamiento del lenguaje, espanol. How do we learn and process inflectional morphology? How do we transform the phonological form of a verb into its inflected form? These questions have attracted particularly contentious consideration over the past twenty years. The controversy raised a debate that applies to many aspects of language processing but has been expressed with specific reference to past-tense English verb processing. The debate refers to the existence of two competing theories found in the literature that try to address the question of how inflected word forms are mentally represented and processed, namely, dual-system and single-system theories. From the connectionist model approach initiated by Rumelhart and McClelland (1986) followed by a critique by Pinker and Prince (1988), many articles have been published to account for regular and irregular verbs in English primarily. …