Introduction: Low back pain is one of the most common complaints in doctors' offices, and acute low back pain is characterized by episodes of pain with less than three weeks duration. The transcutaneous electrical nerve stimulation (TENS), based on the gate control theory of pain proposed by Melzack and Wall in 1965, has been used as an adjunctive therapy in the control of back pain, being a non-invasive, low cost, safe and easy to apply. No studies were found regarding the effectiveness of TENS in acute low back pain.

Objective: To evaluate the effectiveness of TENS in pain management of patients with acute low back pain.

Material and Methods: A randomized clinical trial, double-blinded and placebo-controlled. Patients were selected in the clinics of Federal de University of Sao Paulo (UNIFESP) according to the following criteria: acute low back pain, both genders, aged between 18 and 65 years, pain between 4 and 8cm in pain numeric scale (PNS) and who agreed to participate in the study. After signing the informed consent patients were randomly allocated into one of the groups: TENS group (TG) or Placebo Group (PG). In TG was applied conventional TENS with frequency and intensity variation (FIV) effect, frequency of 100 hertz, a pulse width of 60μs and intensity adjusted according to the individual baseline for each patient without causing muscular contraction. The electrodes were arranged in a cross shape in the paravertebral region (levels T12-L1 and L5 - S1). In PG the same procedures were adopted, but did not occur electrical stimulus. Patients were informed that they could or could not feel electric shocks. Treatment consisted of 10 sessions (2x / week / 5 weeks), with each session lasting 30 '. Assessments were made at the following times: T0 (baseline), T1 to T10 (the beginning and end of each session), T11 (after the last session), T30 (30 days after the last session) and T60 (60 days after the last session). Assessment tools: PNS for pain, short-form 36 (SF-36), Roland-Morris, self-assessment of improvement ("Likert" scale) and drug consumption (daily).

Inclusion Criteria:

• acute low back pain
• both genders
• aged between 18 and 65 years
• pain between 4 and 8cm in PNS (pain numeric scale)
• who agreed to participate in the study.

Exclusion Criteria:

• Patients with pain of inflammatory, neoplastic or infectious origin,
• with cardiac pacemaker,
• previous back surgery,
• signs of irritation of nerve roots,
• vertebral fracture, which changed the physical activity in the last three months,
• and pregnant women