Linguists have increased their documentation efforts in response to the sharp decline in the number of languages. Greater awareness and new sources of funding have led to an upsurge in language documentation. While individual languages make unique contributions to the world’s linguistic heritage, language families, by virtue of their shared heritage, have related contributions to make. The endangerment of entire families, while implied by the loss of language, has not been explored to date. Here, we examine estimates of how many linguistic stocks (the largest subgroups of related languages that are reconstructable) consist entirely of endangered languages and thus are endangered themselves. Our data set includes 372 stocks that had at least one living language in 1950. Our finding is that since that time, 15% of the world’s linguistic stocks have become extinct and another 27% are now moribund in that direct estimates of endangerment indicate that no member languages are being learned by children. For cases where direct estimates were not found, we used population as a proxy for endangerment. If, as many predict, a further 50% of the world’s languages become extinct or moribund in this century, then an additional 25% of the linguistic stocks would be at risk of being lost. If 90% share this fate, only 11% of stocks would have at least one presumably ‘safe’ language. A comparison of the vitality of linguistic stocks by world areas yields the following ranking from worst to best: Americas, Pacific, Asia, Africa, Europe. Finally, some aspects of language that are unique to disappearing language stocks are outlined. Renewed efforts at documenting members of such stocks seem justified.