Speech of late bilinguals has frequently been described in terms of cross-linguistic influence (CLI) from the native language (L1) to the second language (L2), but CLI from the L2 to the L1 has received relatively little attention. This article addresses L2 attainment and L1 attrition in voicing systems through measures of voice onset time (VOT) in two groups of Dutch-German late bilinguals in the Netherlands. One group comprises native speakers of Dutch and the other group comprises native speakers of German, and the two groups further differ in their degree of L2 immersion. The L1-German-L2-Dutch bilinguals (N = 23) are exposed to their L2 at home and outside the home, and the L1-Dutch-L2-German bilinguals (N = 18) are only exposed to their L2 at home. We tested L2 attainment by comparing the bilinguals' L2 to the other bilinguals' L1, and L1 attrition by comparing the bilinguals' L1 to Dutch monolinguals (N = 29) and German monolinguals (N = 27). Our findings indicate that complete L2 immersion may be advantageous in L2 acquisition, but at the same time it may cause L1 phonetic attrition. We discuss how the results match the predictions made by Flege's Speech Learning Model and explore how far bilinguals' success in acquiring L2 VOT and maintaining L1 VOT depends on the immersion context, articulatory constraints and the risk of sounding foreign accented.