|Pyrrhocoroidea (including Largidae: Larginae, Physopeltinae, and Pyrrhocoridae) constitutes the second smallest superfamily of the true bug infraorder Pentatomomorpha (Insecta: Hemiptera: Heteroptera). Although this group includes several taxa widely used as models in experimental studies, as well as a number of economically important pests (inc. cotton stainers), it has received very little attention from the viewpoints of comparative morphology and phylogenetics. To improve this situation and to provide a solid base for future phylogenetic analyses, the morphology of the pregenital abdominal ventrites and trichobothria in 64 out of 70 currently valid genera of Pyrrhocoroidea are examined herein and compared with the closely related outgroups Coreoidea and Lygaeoidea. Also investigated are the fine structure of the trichobothrial complex (especially the bothrium and trichome) and intrageneric, intraspecific and intra-individual variability in the trichobothrial pattern. A new system of abbreviations is proposed to describe particular trichobothrial positions on the abdomen of trichophoran Heteroptera in order to standardise future descriptions. Diagnoses are provided for eachfamily-group taxon in Pyrrhocoroidea and character states of individual genera within these groups demonstrated. The findings are compared with those few phylogenetic hypotheses that are available for Pyrrhocoroidea. The following character states are shared by both Pyrrhocoroidea and Lygaeoidea and partly suggest their sister-group relationship: i) presence of a shallow open bothrium (type B) accompanied by trichome (putative synapomorphy, also present in Hyocephalidae); ii) trichobothria AT5a and AT6a prespiracular (polarity ambiguous); iii) ventral intersegmental suture IV/V incomplete (shared by Physopeltinae, Pyrrhocoridae and Rhyparochromidae; either synapomorphy of Lygaeoidea + Pyrrhocoroidea or homoplasy in individual taxa); iv) presence of ventral laterotergites demarcated by visible tergosternal sutures (symplesiomorphy). No putative synapomorphies on the pregenital abdomen supporting Pyrrhocoroidea as sister to Coreoidea emerged in the study. The family Largidae is diagnosed solely by employing symplesiomorphic character states, while the monophyly of Pyrrhocoridae is strongly supported by three putative synapomorphies: i) segment IV produced forwards submedially anterior to AT4a-c, intersegmental suture III-IV sinuate submedially; ii) AT3c remote from AT3a-b, approaching anterior margin of sternite III; iii) AT5a-c clustered, all prespiracular, situated at the apex of the anterolateral projection of sternite V. Two putative synapomorphies suggest a possible sister-group relationship of Physopeltinae and Pyrrhocoridae: i) mesosternum keeled; ii) sternites V and VI strongly produced anterolaterad, intersegmental sutures IV/V and V/VI incomplete, markedly sinuate laterally. Two competing hypotheses should therefore be tested in future phylogenetic studies of Pyrrhocoroidea: ((Larginae + Physopeltinae) + Pyrrhocoridae) versus (Larginae + (Physopeltinae + Pyrrhocoridae)).