Sialadenosis has been defined as a non-inflammatory, parenchymatous salivary gland disease causing recurrent, bilateral swelling of the salivary glands. As an adverse drug reaction of valproic acid, sialadenosis is very rare. To our knowledge, it has been reported only once in the world literature to date. We present herein the case of a patient with valproic acid-associated sialadenosis of both the parotid and submandibular glands. This appears to be the first published case of a patient who received surgical treatment. On light and electron microscopy of all the affected salivary glands, granular sialadenosis with predominantly moderate electron-dense secretory cytoplasmatic granules was observed. No relevant degenerative alterations were seen. There was no histological evidence of peripheral neuropathy of the nerve supply, leading to disordered activity of acinar cells by loss of neurosecretory granules. Lateral parotidectomy, performed under neuromonitoring control for safety reasons, is the treatment of choice for chronic recurrent parotitis that does not respond to conservative therapy, particularly if the cosmetic deformity is unacceptable to the patient. If the submandibular glands are involved, partial removal is recommended.