Rickets due to dietary calcium deficiency has been well described in black African children, but less is known about this condition in black adolescents. We investigated 26 black adolescents (19 males aged 11 to 19 years and 7 females aged 12 to 15 years) with rachitic leg deformities and 20 controls by routine iliac crest undecalcified cortical bone histomorphometry for disturbances of bone turnover and for mineralization defects, including severity of osteocytic osteolysis (Ot.Olysis) and periosteocytic osteolysis (Peri.Ot.Olysis) of the lacunar‐canalicular space. Serum levels of calcium (sCa), 25‐hydroxyvitamin D (25OHD), 1,25‐dihydroxyvitamin D (1,25(OH)2D), and total alkaline phosphatase (ALP) were measured. Histomorphometry showed varying degrees of severity of secondary hyperparathyroidism (20 HPT) characterized by hyperosteoidosis, increased erosion, and porosis. Because osteoid was neither being mineralized nor eroded (osteoclasts cannot erode osteoid), it increasingly blocked bone surface needed for osteoclastic resorption. Where osteoid covered >50% of bone surface, osteoid thickness, severity of Ot.Olysis, and extent of Peri.Ot.Olysis increased, sCa and 25OHD declined, and 1,25(OH)2D and ALP increased. At 80% osteoid cover, bone remodeling had all but ceased, secondary HPT had changed to osteomalacia, and serum biochemical results had deteriorated further. Disease severity was greater in males than in females, likely because males grow faster and for longer than females. In conclusion, this cross‐sectional clinical case study presents cortical bone histomorphometric data of secondary HPT and its transition to osteomalacia in black adolescents with rickets attributable to dietary calcium deficiency. The bone disease was most severe in older adolescent males. Importantly, bone pathology of calcium deficiency rickets in adolescents was not confined to bone surfaces but also manifested at osteocyte level as Ot.Olysis and Peri.Ot.Olysis. © 2019 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.