A guide catheter for providing access to a patient's cerebrovasculature through an aortic passageway leading from an iliac or femoral location comprising: an axially elongate sheath tube having a distal portion, a proximal portion and a lumen extending therebetween, the proximal portion adapted to extend out of the patient and the distal portion adapted to extend at least to the patient's carotid arteries; the sheath tube comprising at least one diametrically expandable region that comprises a malleable reinforcement structure configured to maintain the at least one diametrically expandable region in a first cross-sectional configuration in which the at least one diametrically expandable region is longitudinally folded into a reduced cross-sectional profile and can be expanded to a second cross-sectional configuration in which the at least one diametrically expanded region is unfolded into a larger cross-sectional profile; a hub coupled to the sheath tube at its proximal end; and a dilator pre-inserted through the lumen in the axially elongate sheath tube, wherein the dilator comprises a length of dilator tubing, a dilator hub comprising a balloon inflation port and a guidewire access port further comprising a hemostasis valve, and a non-compliant balloon, which is deflated and folded about the dilator tubing to form a minimum profile; wherein the dilator is operable to expand the at least one diametrically expandable region from the first, cross-sectional configuration to the second, larger, cross-sectional configuration; wherein the malleable reinforcement structure controls the structural configuration of the diametrically expandable region prior, and subsequent, to expansion, the guide catheter characterized by: an outer, substantially non-distensible layer separated from inner layers of the axially elongate tube except at locations proximal to the proximal end of the expandable region and proximate the distal end of the expandable region, wherein pressurization of the gap separating the inner layers from the outer layer causes inward deformation, collapse, or cross-sectional area reduction of the expandable region, following expansion. an axially elongate sheath tube having a distal portion, a proximal portion and a lumen extending therebetween, the proximal portion adapted to extend out of the patient and the distal portion adapted to extend at least to the patient's carotid arteries; the sheath tube comprising at least one diametrically expandable region that comprises a malleable reinforcement structure configured to maintain the at least one diametrically expandable region in a first cross-sectional configuration in which the at least one diametrically expandable region is longitudinally folded into a reduced cross-sectional profile and can be expanded to a second cross-sectional configuration in which the at least one diametrically expanded region is unfolded into a larger cross-sectional profile; a hub coupled to the sheath tube at its proximal end; and a dilator pre-inserted through the lumen in the axially elongate sheath tube, wherein the dilator comprises a length of dilator tubing, a dilator hub comprising a balloon inflation port and a guidewire access port further comprising a hemostasis valve, and a non-compliant balloon, which is deflated and folded about the dilator tubing to form a minimum profile; wherein the dilator is operable to expand the at least one diametrically expandable region from the first, cross-sectional configuration to the second, larger, cross-sectional configuration; wherein the malleable reinforcement structure controls the structural configuration of the diametrically expandable region prior, and subsequent, to expansion, the guide catheter characterized by: an outer, substantially non-distensible layer separated from inner layers of the axially elongate tube except at locations proximal to the proximal end of the expandable region and proximate the distal end of the expandable region, wherein pressurization of the gap separating the inner layers from the outer layer causes inward deformation, collapse, or cross-sectional area reduction of the expandable region, following expansion.