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. <EOS>