We aimed to explore the nature of verbal repetition deficits and infer the cognitive systems involved in primary progressive aphasia (PPA) and Alzheimer's disease (AD). A total of 63 patients (13 semantic variant (sv-PPA), 17 nonfluent/agrammatic variant (nfv-PPA), 10 logopenic variant (lv-PPA), 23 AD) and 13 matched healthy controls completed a battery of tests that included naming, word comprehension, digit span, repetition of multisyllabic single words, monosyllabic word span presented under similar and dissimilar phonological conditions, and sentence repetition. All patient groups displayed some level of impairment, however, specific patterns emerged in each variant. Participants with sv-PPA were the least impaired, showing marginal difficulties exclusively for sentence repetition, whereas those with lv-PPA had the worst overall performance. Cases with nfv-PPA showed compromised repetition of multisyllabic and phonologically similar words. The deficit in cases with AD was confined to span tasks. These distinctive patterns of language impairments can assist in the differential diagnosis of PPA variants and point toward the vulnerability of specific cognitive systems in each syndrome.