Hyperprolactinemia is the most common abnormality of the hypothalamic-pituitary axis. The aim of this study was to investigate the clinical and radiological features of patients with macroprolactinemia. The study population consisted of patients with elevated serum prolactin (PRL) concentrations who presented to our Endocrinology outpatient clinic. Detection of macroprolactin (macroPRL) was performed using the polyethylene glycol precipitation method. Patients in which macroPRL made up more than 60% of total PRL levels were stratified into the macroPRL group, while the remaining patients were placed in the monomeric prolactin (monoPRL) group. A total of 337 patients were enrolled with a mean age of 33.8 +/- 10.8 (16-66) years and a male/female ratio of 29/308. Eighty-eight of the patients (26.1%) had an elevated macroPRL level. The mean age in the monoPRL group was higher than in the macroPRL group (35.0 +/- 10.1 vs. 30.7 +/- 9.8, P = 0.016). The mean PRL levels (ng/ml) in the macroPRL and monoPRL groups were similar (168.0 +/- 347.0 vs. 238.8 +/- 584.9, P = 0.239). Frequency of amenorrhea, infertility, irregular menses, gynecomastia, and erectile dysfunction were also similar in both groups. More patients in the macroPRL group were asymptomatic compared to the monoPRL group (30.2 vs. 12.0%, P = 0.006). Compared to the macroPRL group, the monoPRL group had a higher frequency of galactorrhea (39.2 vs. 57.1%, P = 0.04) and abnormal magnetic resonance imaging findings (65.3 vs. 81.1%, P = 0.02). Elevated macroPRL levels should be considered a pathological biochemical variant of hyperprolactinemia that may present with any of the conventional symptoms and radiological findings generally associated with elevated PRL levels.