[0053] In some examples, aspiration catheter system 10 is configured to substantially conform to the curvature of the vasculature. In addition, in some examples, aspiration catheter system 10 may have a column strength and flexibility that allows at least the distal portion of aspiration catheter system 10 to be navigated from a femoral artery, through the aorta of the patient, and into the intracranial vascular system of the patient, e.g., to reach a relatively distal treatment site. Alternatively, the elongated body can have a column strength (and/or be otherwise configured) to allow the distal portion of the elongated body to be navigated from a radial artery, through the aorta of the patient or otherwise to a common carotid or vertebral artery-, and into the intracranial vascular system of the patient, e.g., to reach a relatively distal treatment site. [0054] Although primarily described as being used to reach relatively distal vasculature sites, aspiration catheter system 10 may also be configured to be used with other target tissue sites. For example, aspiration catheter system 10 may be used to access tissue sites throughout the coronary and peripheral vasculature, the gastrointestinal tract, the urethra, ureters, fallopian tubes, veins and other body lumens. [0055] In some examples, aspiration catheter system 10 may be described in terms of the working length of an elongated body of outer catheter 12 and/or inner catheter 14. The working length of aspiration catheter system 10 may depend on the location of the target tissue site within the body of a patient or may depend on the medical procedure for which aspiration catheter system 10 is used. For example, if aspiration catheter system 10 is a distal access catheter system used to access vasculature in a brain of a patient from a femoral artery access point at the groin of the patient, the elongated body of outer catheter 12 and/or inner catheter 14 may have a working length of about 115 centimeters (cm) to about 145 cm or more, such as about 130 cm, although other lengths may be used. The distal portion may be about 5 cm to about 35 cm in length. The proximal portion may be about 90 cm to about 130 cm in length, depending on the length of the distal portion. [0056] In some cases, a clinician may steer aspiration catheter system 10 through the vasculature of a patient by pushing or rotating a hub and/or the proximal portion of outer catheter 12 and/or inner catheter 14 to navigate the distal portion of aspiration catheter system 10 through the vasculature of a patient. The clinician may apply torque to the hub and/or the proximal portion of outer catheter 12 and/or inner catheter 14 to rotate the distal portion of the respective outer catheter 12 and inner catheter 14. [0057] Aspiration pump 6 is configured to create a positive pressure (i.e., outflow) on outer catheter 12, e.g., to deliver fluid through an inner lumen of outer catheter 12 into