Background: Primary hypothyroidism can lead to hyperprolactinemia through several mechanisms in both men and women, manifesting as galactorrhoea, loss of libido, and infertility in both sexes, as oligomenorrhea/amenorrhea in women, and as gynecomastia and erectile dysfunction in men. Case presentation: Here presented is a 28-year-old Nigerian woman with a history of recurrent bilateral painless galactorrhoea of 12 years’ duration and persistent low mood. Physical examination was unremarkable. The hormonal assay revealed elevated thyroid-stimulating hormone, elevated serum prolactin, low thyroxine, and low triiodothyronine levels. Magnetic resonance imaging of the brain revealed normal findings. A diagnosis of hyperprolactinemia secondary to primary hypothyroidism was made. Pharmacological therapy began with thyroid hormone replacement therapy and a dopamine agonist: 75 micrograms of levothyroxine daily and 0.5 micrograms of cabergoline twice weekly for 8 weeks. After 8 weeks of pharmacological therapy, hormonal assay revealed values within the reference range with significant symptomatic improvement evidenced by cessation of galactorrhoea and low mood. Conclusion: Primary hypothyroidism has been proven to be one of the numerous causes of hyperprolactinemia and it could be unheeded in a patient who does not present with the typical signs and symptoms of primary hypothyroidism.