Early embryonic development involves complex events such as the regulation of cell division and the establishment of embryonic polarity. To identify genes involved in these events, we collected four-dimensional time-lapse video recordings of the first three cell divisions and analysed terminal phenotypes after RNA interference of 147 embryonic lethal genes previously identified in a systematic screen of Caenorhabditis elegans chromosome I. Over half gave defects in early processes such as meiosis, the assembly or position of the first mitotic spindle, cytokinesis, and proper nuclear positioning. For some phenotypic classes, the majority of genes are involved in a shared biochemical process. In addition, we identified loss-of-function phenotypes for genes of unknown function, but for which homologues exist in other organisms, shedding light on the function of these uncharacterized genes. When applied to the whole genome, this approach should identify the vast majority of genes required for early cell processes, paving the way for a greatly improved understanding of these processes and their regulation at the molecular level.