The high prevalence of autism spectrum disorder (ASD), the specificity of paediatric patients and the determination of their parents give rise to the growing interest of scientists in potential therapeutic approaches. There are multiple aetiological factors involved, and more will probably be discovered. Currently, the involvement of genetic and environmental factors in the aetiology is widely accepted. Growing evidence has been presented for the link between gut dysbiosis and autism. Analysing recent scientific reports, attention was drawn to the proportion and composition of gut microbiota in children with this diagnosis. These are mainly Bacteroidetes, Firmicutes and Actinobacteria, all of which were more abundant in children with ASD than in controls. In turn, children with ASD showed significantly higher counts of Bacteroides, Parabacteroides, Clostridium, Faecalibacterium and Phascolarctobacterium and lower percentages of Coprococcus and Bifidobacterium. If the initial hypotheses support microbial involvement in ASD-related symptoms, clinical trials with microbiota as a therapeutic target would be highly desirable. Recently, researchers have also been interested in faecal microbiota transplantation and microbiota transfer therapy. However, given the inconsistency in results between different centres, final conclusions cannot be reached. Differences in the composition of microbiota arise from, among others, the large age range of patients, which has a general impact on the variability of the microbiome composition over the years of life, environmental diversity with its dietary and cultural habits affecting the unique composition of the microflora, as well as food selectivity that is typically seen in ASD.