A new family of retrotransposons (RTPs) without long terminal repeats (LTRs), designated Q, has been isolated from the malaria vector Anopheles gambiae. The nucleotide sequence of a complete element Q-22, was determined and analysed. Approximately 4.5 kb long, Q-22 contains two long overlapping open reading frames (ORFs) that potentially encode proteins with nucleic acid binding and reverse transcriptase domains similar to those of non-LTR RTPs previously described. The 3' end is characterized by variable numbers of the triplet repeat TAA, immediately following a polyadenylation signal. In situ hybridization of nurse cell polytene chromosomes revealed about twenty labelled sites distributed over all arms and diffuse hybridization to the chromocentre. Cross-hybridizing sequences with the same internal structure occur in all members of the A. gambiae complex. Genomic Southerns of wild A. gambiae specimens probed with Q suggest that Q is or recently was capable of retrotransposition.