Background Idiopathic epilepsy (IE) is the most common cause of repeated seizures in dogs. The International Veterinary Epilepsy Task Force consensus guidelines recommend performing magnetic resonance imaging (MRI) of the brain and cerebrospinal fluid (CSF) analysis as part of a tier II diagnosis of IE, and these procedures have documented risks. The aim of this retrospective study was to identify how often dogs with suspected IE have abnormalities on CSF analysis. Methods Dogs aged between 6 months and 6 years that were presented with a history of two or more seizures with at least 24 h between seizure episodes, a normal neurologic examination, no evidence of toxic or metabolic causes, a normal MRI scan (including contrast administration) and CSF analysis were included. Results Eighty‐two dogs were included. Of these, nine dogs (10.9%) had abnormalities on CSF analysis: five of nine dogs (55.5%) had albuminocytologic dissociation, three of nine dogs (33.3%) had mild increases in total nucleated cell count (TNCC), and one of nine dogs (11.1%) had mild increase in both total protein and TNCC. Cytology in dogs with elevated TNCC revealed a mononuclear pleocytosis. One of the nine dogs with abnormal CSF had a seizure within the 24 h before investigations, and six of nine dogs had a seizure within 1 month before investigation. Conclusion CSF analysis can play an important role in the diagnostic investigation of the underlying causes of repeated seizures. However, in dogs with a normal inter‐ictal neurological examination and MRI scan, it rarely reveals significant abnormalities, and the risk of performing a CSF tap may outweigh the potential diagnostic gain.