The restless legs syndrome (RLS) has repeatedly, but not exclusively, been associated with functional thalamic changes as well as changes in GABAergic neurotransmission. This has been linked to the well-known sensory-motor symptoms, but it has never been investigated whether those factors also account for potential cognitive changes in RLS, even though they are known to play an important role for cognitive control. To investigate the potential relationship between thalamic GABA concentrations and cognitive control in n = 25 RLS patients; a neuropsychological experimental paradigm was used in combination with magnetic resonance spectroscopy (MRS). Compared to n = 31 healthy controls, RLS patients displayed reduced cognitive control capacities, which were most likely based on working memory deficits. On the neurobiochemical level, (relatively) elevated thalamic GABA levels attenuated control deficits only in the RLS group, even though there were no group differences with respect to overall GABA levels. Given that RLS patients are known to display thalamic hyperactivity and associated thalamic hypoconnectivity, (relatively) higher GABA levels may have helped RLS patients to "compensate" for this pathological factor. Our findings specify the functional relevance of thalamic GABAergic neurotransmission for cognition in RLS, even though changes in GABAergic neurotransmission might not be the ultimate cause of control deficits.