Abstract Objective Detection of nerve enlargement in polyneuropathies by sonography is a new research area. No systematic investigation has been done yet in chronic inflammatory demyelinating polyneuropathy (CIDP). Therefore we investigated this in CIDP. Methods Eleven patients with CIDP fulfilling the international criteria on CIDP underwent ultrasonographic examination of the median, ulnar, fibular and posterior tibial nerves and sometimes the brachial plexus bilaterally, using a standardized protocol. We assessed presence of nerve thickening and increased nerve vascularization. Results In 7 of the 11 patients multiple nerve enlargements were detected: ulnar nerve 7, fibular nerve 5, posterior tibial nerve 4 and median nerve in 4 patients. The number of enlarged nerves was related with the MRC sum-score (p=0.03) and the total protein in the cerebrospinal fluid (CSF) at diagnosis (p=0.02). Increased vascularization was seen in 6 of the 11 patients: 4 in one nerve and in 2 in multiple nerves. The number of nerves with increased vascularization was associated with the number of enlarged nerves (p=0.01) and total protein in the CSF (p=0.006). Conclusion Multiple nerve enlargements occur in CIDP showing a relation with a lower MRC sum-score, increased nerve vascularization and a higher total protein of the CSF. Significance Our findings of nerve enlargement and increased nerve vascularization may be tools to monitor disease activity in CIDP, but further studies are needed.