Background and purpose We present the clinical, electrophysiological, and nerve ultrasound findings in cases of persistent carpal tunnel syndrome (PCTS). Methods Eighteen PCTS patients underwent evaluation with the Boston Carpal Tunnel Syndrome Questionnaire (BCTSQ), electrophysiology, and nerve ultrasound with a mean of 3.5 months (SD ± 1.4) after open surgery. Results PCTS patients showed a mean symptom severity scale score of 3.1 (SD ± 1.1) and functional severity scale score of 3.2 (SD ± 0.9) in BCTSQ. Nerve conduction studies revealed axonal affection of the median nerve in 13/18 patients, ultrasound showed disturbed echogenicity in all patients, a pathological wrist to forearm ratio in 16/18 patients, and cross-sectional area enlargement of the median nerve at the distal wrist crease in 12/18 patients. Ultrasound documented scar tissue formation (in 12/18 patients), incomplete release of retinaculum flexorum (in 4/18 patients), and neuroma of the median nerve (in 2/18 patients) as PCTS cause. Conclusion Our data show significant functional disability, axonal nerve damage, and scar tissue formation as common PCTS causes.