BACKGROUND: Bed rest is not only used in the management of patients who are not able to mobilise, but is also prescribed as a treatment for a large number of medical conditions, a procedure that has been challenged. We searched the literature for evidence of benefit or harm of bed rest for any condition. METHODS: We systematically searched MEDLINE and the Cochrane library, and retrieved reports on randomised controlled trials of bed rest versus early mobilisation for any medical condition, including medical procedures. FINDINGS: 39 trials of bed rest for 15 different conditions (total patients 5777) were found. In 24 trials investigating bed rest following a medical procedure, no outcomes improved significantly and eight worsened significantly in some procedures (lumbar puncture, spinal anaesthesia, radiculography, and cardiac catheterisation). In 15 trials investigating bed rest as a primary treatment, no outcomes improved significantly and nine worsened significantly for some conditions (acute low back pain, labour, proteinuric hypertension during pregnancy, myocardial infarction, and acute infectious hepatitis). INTERPRETATION: We should not assume any efficacy for bed rest. Further studies need to be done to establish evidence for the benefit or harm of bed rest as a treatment.