Abstract Since magnetoencephalograms (MEGs) are measurements of the magnetic field produced in the air around the head of electrical sources in the brain, it is possible to measure MEGs on some regular surface over the head such as a plane. Such measurements are easier to make than traditional measurements at a fixed distance from the head. This paper presents results of computer modeling studies of source localization errors caused by using MEGs measured on a plane over the head. It was found that non-spherical head shape does not have a greater effect on localization accuracy for measurements on a plane than for traditional fixed-distance measurements. The source localization errors were less than 1 cm for both types of measurement for sources in the cortical region of the brain. Localization errors were found to increase for sources at greater depth in the brain, but the errors using measurements on a plane were not found to be significantly larger than those using traditional measurements. Hence, because of the ease with which measurements on a plane can be made, more wide-spread use of such measurements should be considered.