A portable chamber for hyperbaric and/or hypoxic treatment comprises an open-ended and typically frustro-conical tubular body sized to accommodate at least one occupant, and two end members configured to be respectively received at opposite extremities of the body for closing the body in a seal tight arrangement. The body of the chamber is made of a flexible yet reinforced elastomeric material such as to be collapsible during transport. One of the end members is provided with a door to provide access to the interior of the chamber. The extremities of the body are substantially spherical such as to receive the correspondingly substantially periphery of the end members. When the chamber is supplied with gases during hyperbaric or hypoxic treatment, the spherical peripheries of the end members are urged against the spherical extremities of the body, thereby providing a seal tight chamber. A treatment system comprising the chamber is also disclosed.