This disclosure describes delivery of omnipolar electrical stimulation with an external electrical stimulator. Omnipolar electrical stimulation may involve stimulation with an electrode carried on the housing of an implantable medical device (IMD) while substantially simultaneously delivering stimulation via one or more implanted electrodes having the same polarity as the electrode on the housing. An external medical device (EMD) may simulate the IMD housing electrode with an electrode separate from the electrodes carried on leads implanted near target tissue. This electrode may be an external electrode carried on the external housing of the EMD or an external patch electrode. Alternatively, the electrode may be an implantable electrode coupled to the EMD. The conductivity of the external or implantable electrode may also be optimized to approximate the conductivity of the IMD housing electrode. This electrode coupled to the EMD may be utilized during trial stimulation or chronic, external, stimulation.