Anammox bacteria exhibit remarkable and characteristic metabolic features that enable them to oxidize ammonium under anoxic conditions. Their ultrastructure is complex, with three compartments, comprising paryphoplasm, the riboplasm and the anammoxosome. The latter is surrounded by ladderane lipids, creating a lipid-surrounded organelle within the riboplasm. In this edition of Molecular Microbiology, van Niftrik and co-workers present detailed ultrastructural investigations that, together with the analysis of the product of a predicted gene and its localization in ultrathin sections, provide the first hints at the way in which these cells divide.