In Escherichia coli, nine gene products are known to be essential for assembly of the division septum. One of these, FtsL, is a bitopic membrane protein whose precise function is not understood. Here we use fluorescence microscopy to study the subcellular localization of FtsL, both in a wild-type strain and in a merodiploid strain that expresses a GFP–FtsL fusion protein. We show that FtsL localizes to the cell septum where it forms a ring analogous to the cytoplasmic FtsZ ring. FtsL localization is dependent upon the function of FtsZ, FtsA and FtsQ, but not FtsI. In a reverse approach, we use fusions of green fluorescent protein (GFP) to FtsZ, FtsA and ZipA to show that these proteins localize to the division site in an FtsL-independent fashion. We propose that FtsL is a relatively late recruit to the ring structure that mediates septation.