Background and Objectives: Immune checkpoint inhibitors (ICIs) have enriched tumor therapy, improving overall survival. Immunotherapy adverse events (irAEs) occur in up to 50% of patients and also affect the peripheral nervous system. The exact pathomechanism is unclear; however, an autoimmune process is implicated. Thus, the clinical evaluation of irAEs in the peripheral nervous system is still demanding. We retrospectively analyzed nerve ultrasound (NU) data of polyneuropathies (PNPs) secondary to checkpoint inhibitors.Materials and Methods: NU data of patients with PNP symptoms secondary to ICI therapy were retrospectively analyzed using the Ultrasound Pattern Sum Score (UPSS) as a quantitative marker. Our findings were compared with a propensity score match analysis (1:1 ratio) to NU findings in patients with chronic inflammatory demyelinating polyneuropathy (CIDP) and chemotherapy-associated PNP patients.Results: In total, 10 patients were included (4 female, mean age 66 ± 10.5, IQR 60–77), where NU was performed in 80%. The UPSS obtained ranged from 0 to 5 (mean 2 ± 1.6, IQR 1–2.5). The morphological changes seen in the NUs resembled sonographic changes seen in chemotherapy-associated PNP (n = 10, mean UPSS 1 ± 1, IQR 0–2) with little to no nerve swelling. In contrast, CIDP patients had a significantly higher UPSS (n = 10, mean UPSS 11 ± 4, IQR 8–13,p< 0.0001).Conclusions: Although an autoimmune process is hypothesized to cause peripheral neurological irAEs, NU showed no increased swelling as seen in CIDP. The nerve swelling observed was mild and comparable to ultrasound findings seen in chemotherapy-associated PNP.