Osteomalacia is the softening and weakening of bones in adults caused by defective mineralisation, most commonly from prolonged vitamin D deficiency that prevents adequate calcium and phosphate absorption. Unlike osteoporosis, where bone mass is lost but mineralisation is normal, osteomalacic bone is poorly calcified and prone to bending, bowing, and pseudofractures. Symptoms include diffuse bone pain, muscle weakness, and difficulty rising from a chair or climbing stairs. At-risk groups include veiled women with little sun exposure, older adults in residential care, people with fat malabsorption, and those on very restrictive diets. Treatment is straightforward: vitamin D repletion with adequate calcium, plus safe sunlight exposure. The childhood equivalent is rickets, and both conditions are entirely preventable, which makes their persistence a marker of health inequality.