This paper focuses on how latent knowledge of an ancestral or heritage language affects subsequent acquisition by adults. The "latent speaker" is defined as an individual raised in an environment where the ancestral language was spoken but who did not become a speaker of that language. The study examines how attitudes, latent knowledge and learning settings affect the subsequent acquisition process of latent speakers of Alaskan Athabascan languages. The first phase of the study focuses on two successful adult learners and their progress towards developing fluency. The second phase includes an analysis of the backgrounds, attitudes and language proficiency of 15 beginning adult heritage language learners. The results suggest that latent speakers have a number of characteristics distinguishing them from other language learners which may both aid and inhibit language learning. Their receptive skills surpass productive skills, they remember common expressions and emotion-laden vocabulary and their productive phonology is advanced. However, these learners tend to have a low estimate of their language abilities and report being hesitant to speak. These results provide information on factors affecting heritage language acquisition and have implications for adult language programmes.