The subject insider trading is controversial. This paper presents series of event studies carried through on the trades with stocks of the firm carried by insiders with the objective to detect abnormal returns, based on the access to privileged information. The sample is composed by trades performed by insiders of the companies with stocks negotiated in the São Paulo Stock Exchange, that are classified as firms with differentiated corporate governance. Indication that trades performed by insiders resulted in abnormal returns compared to the statistically significant expected ones, as in the purchases of common shares; or for selling of preferred stocks.