Introduction: Little is known about treatment of osteoporosis with denosumab (Prolia®) in patients with decreased kidney function. The aim of this retrospective case report study was to investigate effects and side-effects of such treatment. Methods: Since 2012, 75 patients with osteoporosis and decreased kidney function had been treated with denosumab (Prolia®) in the osteoporosis outpatient clinic of the department of endocrinology, Bispebjerg Hospital, University of Copenhagen, Denmark, and data were retrospectively collected from the patient records of these patients in 2021. Results: At baseline, the mean estimated glomerular filtration rate (eGFR) was 34 mL/min (range 9–50) and the median age was 85 years (range 45–103). 95% of the patients had had low-energy fractures, and the bone mineral density T score of the hips was on average − 2.7. All, but one, patients had normal/high parathyroid hormone (PTH) levels. The mean duration of the treatment with denosumab at the follow-up was 5.3 years (range 1.5–10). There was an annual increase of 12% and of 7% in the T score of in the lumbar spine and hip, respectively, compared to the T-scores prior to the denosumab treatment. 20% had a new fracture during the follow-up. 21% had biochemical hypocalcemia following denosumab injection, 7% developed symptoms of hypocalcemia, whereas 4% needed to be hospitalized acutely. Conclusion: Treatment with denosumab of osteoporosis in patients with decreased kidney function (eGFR 9–50 mL/min), with normal/high PTH, seems in general to be well tolerated, with improvement of bone and decreased risk of new fractures.