An apparatus for delivering therapeutic fluid into a body of a patient, comprising: a dispensing unit having a reservoir containing therapeutic fluid, said reservoir having a non-round cross-section, said dispensing unit further comprising: an energy supply means; a driving mechanism and an outlet port, with said driving mechanism causing displacement of the therapeutic fluid disposed inside said reservoir toward said outlet port; a skin adherable needle unit in fluid communication with said dispensing unit; a penetrating cartridge having a penetrating member and a cannula for inserting into the body of the patient; wherein said dispensing unit can be connected to and disconnected from said skin adherable needle unit, said outlet port being configured to connect to and disconnect from said needle unit establishing fluid communication between the reservoir and the cannula via a connecting lumen; and characterized in that: said dispensing unit further comprises: a reusable part having at least part of said driving mechanism and electronic components, and at least one button for controlling operation of said dispensing unit; and a disposable part having said reservoir configured as a unitary portion of a housing of said disposable part; with the energy supply means being electrically coupled to at least one of said electronic components for supplying energy upon connection of said reusable part and said disposable part; and said reservoir has an oval or elliptical cross section and a thin profile having a thickness of about 10mm. a dispensing unit having a reservoir containing therapeutic fluid, said reservoir having a non-round cross-section, said dispensing unit further comprising: an energy supply means; a driving mechanism and an outlet port, with said driving mechanism causing displacement of the therapeutic fluid disposed inside said reservoir toward said outlet port; a skin adherable needle unit in fluid communication with said dispensing unit; a penetrating cartridge having a penetrating member and a cannula for inserting into the body of the patient; wherein said dispensing unit can be connected to and disconnected from said skin adherable needle unit, said outlet port being configured to connect to and disconnect from said needle unit establishing fluid communication between the reservoir and the cannula via a connecting lumen; and characterized in that: said dispensing unit further comprises: a reusable part having at least part of said driving mechanism and electronic components, and at least one button for controlling operation of said dispensing unit; and a disposable part having said reservoir configured as a unitary portion of a housing of said disposable part; with the energy supply means being electrically coupled to at least one of said electronic components for supplying energy upon connection of said reusable part and said disposable part; and said reservoir has an oval or elliptical cross section and a thin profile having a thickness of about 10mm. said dispensing unit further comprises: a reusable part having at least part of said driving mechanism and electronic components, and at least one button for controlling operation of said dispensing unit; and a disposable part having said reservoir configured as a unitary portion of a housing of said disposable part; with the energy supply means being electrically coupled to at least one of said electronic components for supplying energy upon connection of said reusable part and said disposable part; and said reservoir has an oval or elliptical cross section and a thin profile having a thickness of about 10mm.