This paper presents some aspects of the first Portuguese frequency lexicon extracted from a corpus of large dimensions. The Multifunctional Computational Lexicon of Contemporary Portuguese (henceforth MCL) rised from the necessity of filling a gap existent in the studies of the contemporary Portuguese. Until recently, the frequency lexicons of Portuguese were of very small dimensions, such as Português Fundamental, which is constituted by 2.217 words extracted from a 700.000 word corpus and the Frequency Dictionary of Portuguese Words based on a literary corpus of 500.000 words. We describe here the main steps taken for collecting the lexical and frequency data and some of the major problems that arouse in the process. The resulting lexicon is a freely available reliable resource for several types of applications.