A case study investigated the writing processes of an adult native speaker of Portuguese in a number of writing tasks in his native language (L1) and in English, his second language (L2). Writing samples over a 14-month period were examined. Most data were collected in thinking aloud protocols for 10 written tasks of varying degrees of familiarity in the two languages. A post-composing interview concentrating on specific aspects of observed subject writing behavior was conducted after each protocol session. To augment protocol data, observations concerning the nature and quantity of language input and of oral and written language output were gathered. The composing processes used in L1 and L2 were compared and found largely similar, with vocabulary searching the most common interruption of the overall process. The subject used the language of the writing prompt most often for verbalization, notetaking, and transcription, but used L1 more often for side comments. Researcher-subject interaction was almost exclusively in L1. Writing tasks were found to affect writing processes in some ways, and familiarity of the task was also very evident in the writing processes. It is suggested that task importance and familiarity are significant pedagogical considerations. (MSE)