Objective: Research on early cognitive markers of Alzheimer’s disease (AD) is primarily focused on declarative episodic memory tests that involve deliberate and effortful/strategic processes at retrieval. The present study tested the spontaneous retrieval deficit hypothesis, which predicts that people with amnestic mild cognitive impairment (aMCI), who are at increased risk of developing AD, are particularly impaired on tasks that rely on spontaneous retrieval processes. Method: Twenty-three participants with aMCI and 25 healthy controls (HC) completed an easy vigilance task and thought probes (reporting what was going through their mind), which were categorized as spontaneous thoughts about the past (i.e., involuntary memories), current situation, and future (i.e., spontaneous prospection). Results: Participants with aMCI reported significantly fewer spontaneous thoughts or mind-wandering than HC. This effect was driven by significantly fewer involuntary memories, although groups did not differ in the number of current and future thoughts. Conclusions: Findings provide strong support for the spontaneous retrieval deficit hypothesis. Implications for research on mind-wandering and the default network, early cognitive markers of the disease, and our theoretical understanding of the nature of cognitive deficits in AD are discussed.