This paper describes corpus-based analyses of missing translations in simultaneous interpretations. We used English-to-Japanese interpretation data in the simultaneous interpretation database of Nagoya University for the analyses. The English lectures contained 46,568 content words, and 33.1% of them were missing in the translation. We analyzed the relations between omissions and the factors that influence them, i.e., the speech rate of the source language, delay of interpretation, part-of-speech, and depth in the syntactic structure of the source language. The analyses revealed that the proportion of missing translations is high when the speech rate is high, and the delay of interpretation is large, i.e., adverbs were missing in the translations in a high proportion; the words at deeper positions in the syntactic structure were more likely to be missed.