We found voltage-gated potassium channel (VGKC) antibodies in 4 of 15 patients with limbic encephalitis (LE). Two patients with idiopathic LE had high VGKC antibody levels (>800 pM; controls <100 pM), that fell in parallel with a clinical response to immunotherapy. Two patients with lower VGKC antibodies (170 pM, 300 pM) had lung cancer (radiological evidence only in one) and the LE improved with immunotherapy in one. The other 11 patients without VGKC antibodies had paraneoplastic LE and eight onconeural antibodies (Hu in 6; Ma2 in 2). VGKC antibodies do not unambiguously discriminate between idiopathic or paraneoplastic LE but probably indicate a good response to immunotherapy.