Alternative splicing is widespread throughout eukaryotic genomes and greatly increases transcriptomic diversity. Many alternative isoforms have functional roles in developmental processes and are precisely temporally regulated. To facilitate the study of alternative splicing in a developmental context, we created MeDAS, a Metazoan Developmental Alternative Splicing database. MeDAS is an added-value resource that re-analyses publicly archived RNA-seq libraries to provide quantitative data on alternative splicing events as they vary across the time course of development. It has broad temporal and taxonomic scope and is intended to assist the user in identifying trends in alternative splicing throughout development. To create MeDAS, we re-analysed a curated set of 2232 Illumina polyA+ RNA-seq libraries that chart detailed time courses of embryonic and post-natal development across 18 species with a taxonomic range spanning the major metazoan lineages from Caenorhabditis elegans to human. MeDAS is freely available at https://das.chenlulab.com both as raw data tables and as an interactive browser allowing searches by species, tissue, or genomic feature (gene, transcript or exon ID and sequence). Results will provide details on alternative splicing events identified for the queried feature and can be visualised at the gene-, transcript- and exon-level as time courses of expression and inclusion levels, respectively.