The ionic aggregates in an as-extruded and a recrystallized poly(ethylene-ran-methacrylic acid) ionomer melt neutralized with sodium have been imaged using scanning transmission electron microscopy (STEM). The recrystallized sample exhibits a macrophase-separated structure with three phases,with distinct boundaries. Phase I does not contain aggregates > 1 nm, phase II contains small spherical aggregates of similar to2-15 nm in diameter, and phase III contains large aggregates with diameters ranging from similar to20 to 160 nm. Contrast reversal between bright field and annular dark field STEM images indicates that the aggregates are Na-rich. In contrast, the as-extruded sample is featureless on the STEM length scale. This study shows that thermal history has a major impact on ionomer morphology. X-ray energy dispersive spectroscopy (XEDS) using a 1 nm probe confirms higher Na contents in the ionic aggregates and detects Na in the matrix. XEDS also finds a significant amount of C in the ion-rich aggregates due to the incorporation of PE and unneutralized MAA monomers into the aggregates. The observed phase separation in the recrystallized sample complicates the interpretation of scattering and spectroscopic data, but we attempt to reconcile our findings with,previous studies.