The subject of this study was a Peruvian child who learned German first and, from the age of 2 years and 10 months, was systematically exposed to Spanish. At the age of 4, he had mastered both German and Spanish to the same degree of phonic, morphological, and syntactic competence. Two weeks after the surgical removal of a brain tumor at 5 years of age, the child began to develop a motor aphasia, followed by a sensory aphasia, caused by new brain lesions. Loss of speech occurred in the form of a gradual decrease in the frequency of utterances to zero, affecting both languages at the same time, which confirmed the hypothesis that the child had acquired a coordinate bilingualism. Among the hypotheses concerning bilingualism offered as a result of this case study are the following: (1) A bilingual education favors the development of cognitive and affective qualities in a child. (2) A bilingual education can result in the development of a coordinate bilingualism. (3) To develop coordinate bilingualism, it is recommended that the child learn one language first and begin learning the other at the age of 3 years and several months. (4) The first language should be the one spoken by the parents. (5) Both parents should speak to the child in the same language. (Author/PP)