This paper presents a robotized tele-echography system with an assisting visibility mode that helps the medical expert diagnosis. This autonomous mode is based on a multitask control approach that maintains the visibility of an anatomic element of interest while the medical expert tele-operates a 2D ultrasound probe held by a 4-DoF robot. The main task is used to automatically maintain several visual constraints that guarantee an intersection between the US image plane and the organ of interest. A secondary task allows the medical expert to manually apply the probe motion through the tele-operation mode. The main advantage of this approach is to give to the clinician the control of all the degrees of freedom of the probe to examine the patient while automatically preserving the visibility of the organ of interest when required. Experimental results, performed on a phantom and human abdomen, demonstrate the efficiency of the visibility assistance task.