Thyroid diseases may cause signs and symptoms of neuromuscular dysfunction. Hypothyroidism has been associated with the clinical features of proximal muscle weakness, mononeuropathy, and sensorimotor polyneuropathy. This study aimed at evaluating the electrophysiologic findings in patients with untreated spontaneous hypothyroidism and comparing them with a healthy control group. In a case-control cross-sectional study, 40 patients with definite diagnosis of clinical hypothyroidism and 40 healthy control subjects were evaluated by electromyography and nerve conduction studies in the specialized clinic of the Tabriz University of Medical Sciences during an 18-month period. Seven male and 33 female patients with a mean age of 39.5 ± 11.8 years were enrolled. In this group, there were 12 cases (30%) with clinical muscle weakness, with severity of approximately 4/5, 18 cases (45%) with decreased or absent deep tendon reflexes, 6 cases (15%) with neuropathy, including 4 sensory and 2 sensorimotor, of which 5 cases were mild and 1 case was moderate, 3 cases (7.5%) with myopathy, and 13 cases (32.5%) with carpal tunnel syndrome, which was mild in 7, moderate in 10, and severe in 2 hands. Patients with neuropathy were significantly older than those without neuropathy (P = 0.001). There was no significant relation between gender, duration of the disease, serum TSH level, and the presence of clinical muscle weakness with the occurrence of neuropathy or myopathy. Female gender, increasing age, duration of the disease, and the frequency of clinical weakness were, however, significantly related to the presence of carpal tunnel syndrome (P < 0.05). In conclusion, in patients with untreated primary hypothyroidism, majority had the carpal tunnel syndrome. Mild neuropathy mainly of sensory type and myopathy were uncommon and rare findings, respectively. Early treatment would hinder the progression of mentioned abnormalities and minimize their occurrence.