How stable or how permeable to attrition are a multilingual’s first and second languages during life periods characterized by dynamic changes in language-use frequencies? This longitudinal study sheds some light on this issue by investigating changing patterns in a multilingual speaker’s tip-of-the-tongue (TOT) states. Over a period of 10 years, the multilingual recorded more than 100 TOT states, together with 400 non-target word associations, as they occurred with words from the speaker’s five languages (L1 German, L2 Russian, L3 English, L4 Spanish, and L5 Portuguese). During the period, the L1 was consistently used less than the L3 and L4, providing a setting in which L1 attrition might occur. Data were analyzed with respect to the changing frequencies of TOT state occurrence in the different languages, the contribution of each language to the word associations generated during word search, the typological relatedness of targets and associates, and the linguistic context of initial learning of each language. Rates of TOT states and percentages of cross-language word associations and within-language word associations fluctuated in response to dynamic patterns of language use and maintenance, demonstrating the value of data on word-retrieval failure for studies of language attrition. The data reveal that the speaker’s L1 appeared to gain stability after an early period suggestive of attrition, despite low frequency of use overall. This finding supports the view that the L1 is exceptional, highly resistant to attrition, but also suggests that temporary impairment of L1 can occur when a multilingual speaker’s overall set of interacting language systems comes out of balance.