This paper is based upon a longitudinal study of L2 attrition in a bilingual child who grew up in an L2 migration background (Germany) and moved to the country of origin (Portugal) at the age of nine, experiencing a "dominance shift from the L2 to the L1." The study aims to analyze the effects of language loss in L2 German. Data collection started 3 weeks after the child's immersion in the Portuguese setting and ended 18 months later. Results show first effects of language attrition after 5 months of reduced exposure to German; 18 months later the informant showed severe word retrieval difficulties and was unable to produce complete sentences in her L2. The findings thus confirm the conclusions of other studies on child language attrition, which attest to strong effects of attrition when the loss of contact with the target language occurs in childhood.