Autism is a developmental disorder marked by possible altered sensory responsivity to external stimuli. Naturalistic functional magnetic resonance imaging is a useful way to characterize brain activity using real-life dynamic stimuli (e.g., movie-watching). Inter-subject functional connectivity (ISFC) is sensitive to the stimulus-driven neural coupling across individuals and appears to track individual changes in psychiatric symptoms. Here, we compared ISFCs in groups of autistic (AUT) and neurotypical (NT) participants from two datasets from two countries using similar sets of short movie stimuli (German dataset, visual-only: NNT = 25, NAUT= 22; Finnish dataset, audiovisual: NNT = 19, NAUT = 18). ISFC was calculated between 273 regions of interest, covering the whole brain. Significance of group differences was evaluated with subject-wise permutations in the two datasets. Both datasets showed reliable ISFCs between visual, auditory (only in audiovisual data), posterior temporal, and parietal regions. The peak ISFCs were lower in AUT compared with NT adults in similar brain regions in both datasets. In the Finnish sample, the group differences and the level of ISFC were higher in the audiovisual data. This difference is partly related to the absence of soundtrack of German movie stimuli, explaining differences in regions sensitive to sound and speech (e.g., superior and middle temporal regions), but was also observed in other brain areas. Although the regional group differences were qualitatively similar in both datasets, only a subset of group differences was replicated in specific connections in both datasets. Thus, these findings should be replicated in larger samples in the future.