We describe the identification and characterization of circular intronic long noncoding RNAs in human cells, which accumulate owing to a failure in debranching. The formation of such circular intronic RNAs (ciRNAs) can be recapitulated using expression vectors, and their processing depends on a consensus motif containing a 7 nt GU-rich element near the 5' splice site and an 11 nt C-rich element close to the branchpoint site. In addition, we show that ciRNAs are abundant in the nucleus and have little enrichment for microRNA target sites. Importantly, knockdown of ciRNAs led to the reduced expression of their parent genes. One abundant such RNA, ci-ankrd52, largely accumulates to its sites of transcription, associates with elongation Pol II machinery, and acts as a positive regulator of Pol II transcription. This study thus suggests a cis-regulatory role of noncoding intronic transcripts on their parent coding genes.