Expression of microRNAs (miRNAs) is characteristically altered in cancer, and they may play a role in cancer development and progression. The authors performed microarray and real-time quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) analyses to determine the miRNA expression profile of primary small cell lung cancer. Here we show that at least 24 miRNAs are differentially expressed between normal lung and primary small cell lung cancer (SCLC) tumors. These include miR-301, miR-183/96/182, miR-126, and miR-223, which are microRNAs deregulated in other tumor types as well; and other miRNAs, such as miR-374 and miR-210, not previously reported in association with lung cancer. The aberrant miRNA profile of SCLC may offer new insights in the biology of this aggressive tumor, and could potentially provide novel diagnostic markers.