Positron emission tomography (PET) is a molecular imaging technique which is now widely established as a powerful tool for diagnosing a variety of cancers. However, PET images are substantially degraded by respiratory motion, to the extent that this may adversely impact upon subsequent diagnosis. A motion correction and attenuation correction method is proposed to align the gated PET images and then correct for attenuation. Experimental results show that this method can effectively correct for respiratory motion and improve PET image quality.