Deficits in cognitive control have been linked to intrusive memories after traumatic life events as well as rumination. However, causal relations are still unclear. Causality can be investigated by directly influencing a brain region associated with cognitive control via transcranial direct current stimulation (tDCS). In this study, we investigated the effects of tDCS over the left dorsolateral prefrontal cortex (dlPFC) on one aspect of cognitive control—resistance to proactive interference (PI)—as well as on intrusive memories and rumination. Using a between-subject design, we expected active tDCS to affect intrusive memories and rumination by influencing resistance to PI. N = 118 healthy individuals completed the modified California Verbal Learning Test twice, once without stimulation and once during 20-min tDCS (anodal, cathodal, or sham). Following tDCS, participants watched a trauma film; afterwards, intrusive memories and rumination were assessed. TDCS neither affected resistance to PI nor film-related intrusive memories or rumination. Furthermore, individuals with low resistance to PI did not experience more intrusive memories or rumination. These results question the role of the left dlPFC as well as the well-established link between resistance to PI and intrusive memories. Future studies are needed to replicate these findings and to address possible methodological shortcomings of this study.