microRNAs (miRNAs) are approximately 22-nucleotide small RNAs that act as endogenous regulators of gene expression by base-pairing with target mRNAs. Here we analyze the function of the six members of the Caenorhabditis elegans miR-51 family of miRNAs (miR-51, miR-52, miR-53, miR-54, miR-55, miR-56). miR-51 family miRNAs are broadly expressed from mid-embryogenesis onward. The miR-51 family is redundantly required for embryonic development. mir-51 family mutants display a highly penetrant pharynx unattached (Pun) phenotype, where the pharyngeal muscle, the food pump of C. elegans, is not attached to the mouth. Unusually, the Pun phenotype in mir-51 family mutants is not due to a failure to attach, but instead a failure to maintain attachment during late embryogenesis. Expression of the miR-51 family in the mouth is sufficient to maintain attachment. The Fat cadherin ortholog CDH-3 is expressed in the mouth and is a direct target of the miR-51 family miRNAs. Genetic analysis reveals that miR-51 family miRNAs might act in part through CDH-3 to regulate pharynx attachment. This study is the first to assign a function to the miR-51/miR-100 miRNA family in any organism.