Nonuniform aperture synthesis radiometers (NASRs) are emerging in Earth remote sensing. The main disadvantage of NASRs is the complexity of the image reconstruction. In this letter, the gridding method is introduced as an efficient method to reconstruct brightness temperature images for NASRs. In the gridding method, a Voronoi diagram is applied to dividing the sampling region in the spatial frequency domain into a number of small cells, and the area of each cell is regarded as the density compensation factor. Meanwhile, a method is proposed to produce the outermost Voronoi cells for the outermost visibility samples. The errors induced by using the gridding method are analyzed. The nonuniformity factor (NF) is defined to indicate the nonuniformity of a sampling pattern. The numerical results verify that the gridding method can be applied to image reconstruction for NASRs and that the accuracy of reconstructed images is dependent on NF. The comparison between the gridding method and the nonuniform fast Fourier transform algorithm shows that the gridding method has lower computational complexity.