Acute low back pain is evolving for less than 4 or 6 weeks. The diagnostic stake in front of an acute low back pain is not to ignore a condition requiring a specific treatment (vertebral fracture, tumours, infections, inflammatory diseases...). Signs of alerts from patient history are to be looked for to enable it. Once the diagnosis of non specific low back pain has been confirmed and in absence of neurological complications, the therapeutic stake is to avoid chronicity by a treatment adapted to every patient. Numerous scientific quality data questioned the interest of the bed rest for non specific acute low back pain and the beneficial role of the preservation of the activities to avoid chronicity. The interest to inform and to reassure the patient on his future is also an important condition of the care.