Back orthosis for stabilizing a patient's back, comprising: a back member having a stabilizing body and supporting the back, a hip strap assembly connected to the back member for attaching said orthosis close to the patient's hips, and a shoulder strap assembly having at least two shoulder pull straps (42, 44), wherein each shoulder pull strap (42, 44), when being attached to the patient, is guided from the back member to the hip strap assembly over a shoulder of the patient and through at least one deflection member arranged on the back member, and can be coupled or is coupled to the hip strap assembly, wherein the two shoulder pull straps (42, 44) comprise two portions, wherein the two shoulder pull straps (42, 44) further comprise at least one upper shoulder strap portion that extends from the back member over the shoulders, and at least one lower shoulder strap portion that extends from the upper shoulder strap portion to the hip strap assembly via the deflection member arranged on the back member, and wherein the at least one upper shoulder strap portion of one of the two shoulder pull straps (42, 44) and the at least one lower shoulder strap portion of said shoulder pull strap (42, 44) are connectable to one another via a connecting member so that the length of at least one of the shoulder pull straps (42, 44) is adjustable, and wherein the shoulder strap assembly is connected to the hip strap assembly via at least one guide member, characterized in that the guide member is a deflection buckle allowing to adjust the length of the lower shoulder strap portion, and that the position of the deflection member relative to the back member is variable. a back member having a stabilizing body and supporting the back, a hip strap assembly connected to the back member for attaching said orthosis close to the patient's hips, and a shoulder strap assembly having at least two shoulder pull straps (42, 44), wherein each shoulder pull strap (42, 44), when being attached to the patient, is guided from the back member to the hip strap assembly over a shoulder of the patient and through at least one deflection member arranged on the back member, and can be coupled or is coupled to the hip strap assembly, wherein the two shoulder pull straps (42, 44) comprise two portions, wherein the two shoulder pull straps (42, 44) further comprise at least one upper shoulder strap portion that extends from the back member over the shoulders, and at least one lower shoulder strap portion that extends from the upper shoulder strap portion to the hip strap assembly via the deflection member arranged on the back member, and wherein the at least one upper shoulder strap portion of one of the two shoulder pull straps (42, 44) and the at least one lower shoulder strap portion of said shoulder pull strap (42, 44) are connectable to one another via a connecting member so that the length of at least one of the shoulder pull straps (42, 44) is adjustable, and wherein the shoulder strap assembly is connected to the hip strap assembly via at least one guide member, characterized in that the guide member is a deflection buckle allowing to adjust the length of the lower shoulder strap portion, and that the position of the deflection member relative to the back member is variable.