The treatment strategy for nonfunctioning pituitary adenomas (NFPA) includes surgery, radiotherapy, medical treatment, or follow-up. Prior series of patients with NFPAs followed without intervention include small numbers of patients with macroadenomas. This study investigated the natural history of patients with macroadenomas followed without treatment. Retrospective cohort study included patients>18 years, with a diagnosis of NFPA ≥ 10 mm who were naïve to surgery or medical treatment and followed more than 12 months after diagnosis. Patients with chiasmal threat were excluded. Follow-up terminated if the patient underwent surgery, received cabergoline or was lost to follow-up. Data collected included evaluation of tumour characteristics and size by MRI, symptoms including visual disturbances, and hormonal levels. Tumour growth was defined as maximal diameter increase of ≥2 mm. The cohort included 49 patients (30 males, mean age 68.0 ± 12.0 years). At diagnosis, the average tumour size was 17.8 ± 5.9 mm. Mean follow-up time was 4.9 ± 4.9 years. Increase in tumour size occurred in 16 patients (33%), with an average growth of 5.1 ± 4.4 mm. Reduction in tumour size occurred in 10 patients (20%), with a mean decrease of 3.5 ± 1.3 mm. Twenty-three patients remained with stable tumours. Overall, 33 patients (67%) were observed without any intervention; 3 patients were operated and 13 were treated with cabergoline. None of the parameters including age, gender, baseline tumour size, invasiveness, visual disturbances, or hypopituitarism at diagnosis, predicted tumour growth. Observation of NFPAs without surgery or medical therapy is a reasonable approach in selected patients. In our study, no parameter predicted tumour growth.