Background: Semantic cognition depends on (a) semantic representations that code knowledge and (b) executive control processes that regulate access to this information such that relevant aspects are brought to the fore. It is not clear whether this second element, termed semantic control, draws on the same resources as executive processing in other domains. Aims: We investigated the degree of independence between semantic control and domain-general executive function by studying non-semantic executive control in three patients who had semantic control deficits, and problems maintaining task-relevant conceptual knowledge in working memory. Methods & Procedures: Patients completed (a) a phonological working memory task that manipulated executive demands and (b) a series of working memory tasks that loaded a variety of executive functions: updating information, dividing attention, and manipulating the contents of working memory. These tasks featured digits and letters, placing minimal demands on semantic processing. Outcomes & Results: While two patients displayed clear executive deficits on these non-semantic tasks, the third case (patient JB) showed fully intact non-semantic control despite a clear control deficit for semantic tasks. Conclusions: This dissociation suggests that executive control over semantic knowledge relies on partially distinct neural mechanisms to those involved in domain-general control. © 2013 Copyright Taylor and Francis Group, LLC.