Attenuation correction is required in positron emission tomography for accurate quantitation and to reduce artifacts. In previous work, we have shown that consistency information can be used to perform attenuation correction in the absence of any transmission measurements. In the previous work, a separate object was used for each slice and was transformed in two dimensions. Here, we introduce an extension that performs three-dimensional transformations on a single object over many slices. The aim is to produce a useful attenuation correction in situations where either it is impractical to acquire transmission data or there is significant misregistration between the transmission and emission data. Results are presented for simulated test cases with uniform and nonuniform attenuation and experimental cardiac phantom data. The algorithm as it stands is too unstable to allow for accurate attenuation correction without any transmission measurements. However, it may be useful for correcting misregistration, and may possibly be extended to perform coregistration.