We conducted a multi-pronged investigation of different types of reporting bias in autism early childhood intervention research. First, we investigated the prevalence of reporting failures of completed trials registered on clinicaltrials.gov, and found that only 7% of registered trials were updated with results on the registration platform and only 64% had associated published reports. Next, we investigated the extent to which inadequate reporting prevents inclusion in meta-analytic summary estimates by identifying reports of studies that were eligible for inclusion in a prior meta-analysis, and found that 25% were excluded due to inadequate reporting. Finally, we investigated selective reporting practices by analyzing the protocols of the studies included in the meta-analysis which had been registered on any trial registry and coding their timing, completeness, and consistency. We found that 23% of studies were pre-registered, 71% were late-registered, and 5% were registered at an unclear date. Only 8% of registrations specified all of the necessary components. Evidence of selective reporting was common; 36% failed to report a registered outcome, 61% reported unregistered outcomes, 23% switched primary and secondary outcomes, and 43% had assessment timepoints that differed from registration specification. Given the inadequacy of registration and reporting practices, we offer practical recommendations to facilitate improvement for the field of autism research.