Distinguishing autism spectrum behaviours from behaviours relating to disorganised attachment can be challenging. There is, for instance, a notable overlap between both conditions in terms of behaviours deemed stereotypical. In addition, there are also similarities regarding some atypical social overtures. Responding to this overlap has been the subject for much debate in the literature. Disorganised attachment was first introduced and conceptualised by the attachment researcher, Mary Main. Main is considered the leading authority on coding this phenomenon. During the course of archival research, we obtained Main’s notes on coding attachment in a group of fifteen children with autism spectrum conditions (hereafter ASC). Drawing on these texts, this paper explores Main’s reasoning when making distinctions between ASC and attachment at the behavioural level. Our approach is informed by Chang’s (2017) argument for the potential of “history as complementary science. Analysis indicate that, for Main, frequency and timing was an important differential factor when attributing a behaviour to either ASC or the child’s attachment pattern.