Aim: to investigate the risk factors for severe hypocalcemia (SH) after parathyroidectomy (PTx) in dialysis-treated CKD stage 5D patients with secondary hyperparathyroidism. Materials and methods: we performed a retrospective cohort study included 318 severe SHPT dialysisdependent patients who underwent successful subtotal or total PTx with autotransplantation of parathyroid tissue. Severe postoperative hypocalcemia was defi ned as an ionized serum calcium level less than 0.9 mmol/l on a day 2 after surgery. Results:The incidence of early postoperative SH in our cohort was 66% (210 from 318). Univariate analysis showed that SH patients in comparison with non-SH group were signifi cantly younger (44 [37; 54] vs 52 [43; 59] years, ?<0.0001), had higher baseline PTH (134 [99.6; 185] vs 89 [67.5; 114] pmol/l, ?<0.0001) and alkaline phosphatase (AP) levels (380.6 [191; 681] vs 130 [96; 175] IU/l, ?<0.0001), lower baseline serum total calcium (Ca) level (2.46±0.22 vs 2.57±0.21 mmol/l, ?<0.0001) and ionized Ca (1.2 [1.11; 1.28] vs 1.28 [1.21; 1.36] mmol/l, ?<0.0001), higher ΔPTH before/after surgery (126 [90.6; 175] vs 81.1 [60; 105.1], ?<0.0001). The multivariate logistic regression revealed AP level as the only independent risk factor of severe hypocalcemia development after PTx (OR 3.8 [1.7; 8.2] per each 100 IU/l, ?=0.001). Sex, dialysis vintage, RRT modality (hemodialysis or peritoneal dialysis) and type of surgery were not associated with risk of SH (?=0.55, 0.21, 0.27 and 0.81, respectively). In nested models excluding AP signifi cant factors of postoperative SH were preoperative PTH (OR 1.03 [1.02; 1.032] per each pmol/l, ?<0.001), ΔPTH before/after surgery (OR 1.03 [1.02; 1.034] per each pmol/l, ?<0.001), age (OR 0.96 [0.94; 0.99] per a year, ?=0.003), baseline total serum Ca (OR 0.2 [0.05; 0.78] per each mmol/l, ?=0.021). The length of hospital stay was signifi cantly longer in SH patients (?=0.0016). Conclusions: the preoperative AP level was the most important predictor of the development of severe postoperative hypocalcemia in patients after PTx due to secondary hyperparathyroidism. In addition, important risk factors may include young age, low baseline total calcium levels, high PTH levels before surgery.