A cladistic analysis of the tribe Agathidiini Westwood is presented. Agathidiines are slime mould specialists and they are hypothesized to be a monophyletic group consisting of 12 genera (Afroagathidium Angelini & Peck, Agathidium Panzer, Anisotoma Panzer, Besuchetionella Angelini & Peck, Cyrtoplastus Reitter, Decuria Miller & Wheeler, Gelae Miller & Wheeler, Liodopria Reitter, Pseudoagathidium Angelini, Sphaeroliodes Portevin, and Stetholiodes Fall), based on three synapomorphies: epipleuron present to apical third, mesoventrite without longitudinal carina and longitudinal setal lines present on the tibiae. The dataset for phylogenetic analysis comprised 72 characters representing 198 character states derived from adult morphology. These data were analysed using equal weighting and implied weighting (k = 1–6) and supported the monophyly of the tribe based on three unique characters (epipleuron present to apical third, mesoventrite without longitudinal carina, longitudinal setal lines present on tibia) and two homoplastic characters [antennomeres 7–10 (or 6–9) asymmetrical, apical shape of terminal antennomere abruptly tapered]. The topology of IW trees with k = 4–6 was identical with one of three EW trees. Decuria was sister group to the remaining agathidiine genera whereas the following groups were resolved as monophyletic: Anisotoma, Gelae + Liodopria, and Pseudoagathidium (Afroagathidium + Besuchetionella). The clade [Sphaeroliodes rufescens (Agathidium bockshini, Agathidium subcostatum)] was supported in all analyses except for the IW (k = 1) cladogram. The monophyly of Agathidium was not supported at all and was rendered paraphyletic by the placements of Sphaeroliodes, Stetholiodes and the Pseudoagathidium (Afroagathidium + Besuchetionella) clade. Sphaeroliodes is synonymized with Agathidium (syn.n.) resulting in two new combinations [A. acuminatus (Švec) and A. rufescens (Portevin)]. Contractability is a complex character composed of several morphological features that have evolved independently within the agathidiine tree. Conglobation (the ability to roll the body into a ball) has arisen at least twice in Agathidiini.