We reported accentuated lactational decreases in areal bone mineral density and only partial skeletal recovery after lactation in Ugandan women with HIV (WWH) initiated on tenofovir disoproxil fumarate-based antiretroviral therapy (TDF-based ART) during pregnancy compared to women without HIV (REF). WWH also had higher breast milk calcium in the first months of lactation. To investigate the mechanisms, we measured bone turnover markers (bone resorption: C-terminal telopeptide [CTX]; bone formation: procollagen type 1 N-terminal propeptide [P1NP], bone-specific and total alkaline phosphatase [BALP, TALP]), hormones (parathyroid hormone [PTH], intact fibroblast growth factor 23 [FGF23], 1,25-dihydroxyvitamin D [1,25(OH)2 D]), vitamin D status (25-hydroxyvitamin D [25OHD]), and indices of mineral metabolism and renal function. Blood and urine samples collected at 36 weeks of gestation, 14 and 26 weeks of lactation, and 3-6 months after lactation were analyzed. Mean 25OHD was >50 nmol/L throughout. Both groups experienced similar biochemical changes during pregnancy and lactation to women in other settings, but within these patterns, the two groups differed significantly. Notably, WWH had higher PTH (+31%) and lower 1,25(OH)2 D (-9%) and TmP/GFR (-9%) throughout, lower P1NP (-27%) and plasma phosphate (-10%) in pregnancy, higher CTX (+15%) and BALP (+19%), and lower eGFR (-4%) during and after lactation. P1NP/CTX ratio was lower in WWH than REF in pregnancy (-21%), less so in lactation (-15%), and similar after lactation. Additionally, WWH had lower plasma calcium (-5%), lower FGF23 (-16%) and fasting urinary calcium (-34%) at one or both lactation timepoints, and higher fasting urinary phosphate (+22%) at 26 weeks of lactation and after lactation. These differences resemble reported TDF effects, especially raised PTH, increased bone resorption, decreased bone formation, and decreased renal function, and may explain the observed differences in bone mineral density and breast milk calcium. Further studies are needed to determine whether HIV and TDF-based ART have long-term consequences for maternal bone health and offspring growth. © 2023 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).