Rheumatic diseases in childhood and adolescence can lead to secondary osteoporosis based on various pathophysiologies. The underlying disease, medication and immobility resulting in a reduced osteoanabolic stimulus contribute to the development of a fragile skeletal system. For diagnostic purposes dual-energy X-ray absorptiometry (DXA) is the most frequently used technology. For interpretation of the areal bone mineral density, age and gender matched reference data have to be used. Particularly in the pediatric field, body height must additionally be taken into consideration. Further techniques which can provide detailed information are peripheral quantitative computed tomography and high resolution magnetic resonance imaging. Nowadays, skeletal assessments have to be interpreted in the context of the muscular system. The concept of the functional muscle-bone unit is widely accepted and uses the muscles as the dominating factor. In a second step the adaptation of the skeletal system to the applied muscle force is evaluated. This allows a differentiation between primary and secondary skeletal diseases depending on the ratio of muscles to bone. Therapeutic options for secondary osteoporosis include reduction of the causative medication, treatment of the underlying disease, antiresorptive treatment with bisphosphonates and different programs to activate the muscles. A multimodal interval rehabilitation program including alternating side vibration shows positive effects on mobility, muscle function and bone mass in children and adolescents.