Objective: To date, efforts to reliably manipulate the immune system to promote tumor regression in the brain have been disappointing. We report a unique experience of successful immunotherapy to treat a pituitary macroprolactinoma. Methods: A 31-year-old woman with an established history of pituitary macroprolactinoma who had undergone tumor resection followed by radiation was admitted to our clinic. The diagnosis had been made due to the patient’s symptoms, a serum prolactin (PRL) level of 29,600 mIU/l, a brain MRI revealing a 23 × 19 × 18 mm pituitary mass and a positive PRL immunohistochemistry of the mass. Six months following surgery, she reexperienced headache, excessive sweating and a serum PRL concentration of 2,960 mIU/l despite receiving 30 mg/day bromocriptine. Brain MRI revealed a pituitary mass (3 × 6 × 8 mm) compatible with a pituitary adenoma. Twenty micrograms per milliliter of G2 (as a T helper 1 activator adjuvant) was inoculated intradermally once per week for 24 consecutive weeks (each injection contained 10 µg of G2). The autoantigens were inoculated at the same time with G2. Results: After immunotherapy, serum PRL concentration decreased to 82 mIU/l, the patient’s symptoms disappeared, skin thickness increased to normal and bromocriptine dosage was tapered to 20 mg per week. A follow-up brain MRI revealed almost complete disappearance of the tumor. The patient does not complain of any problems at 1-year follow-up. Conclusion: Activation of both nonspecific (natural killer cells) and specific (cytotoxic T lymphocytes) immunity in relation to the T helper 1 cytokine network is a promising strategy for the treatment of tumors of the central nervous system in humans, especially pituitary macroprolactinomas.