BL Cam is an extreme metal-de?cient ?eld high-amplitude SX Phe-type variable where a very complex frequency spectrum is detected, with a number of independent nonradial modes excited, unusual among the high-amplitude pulsators in the Lower Classical Instability Strip. Aims. An extensive and detailed study has been carried out to investigate the pulsational content and properties of this object. Methods. The analysis is based on 283 h of CCD observations obtained in the Johnson V ?lter, during a long multisite photometric campaign carried out along the Northern autumn-winter of 2005–2006. Additionally, multicolour BI photometry was also collected to study the phase shifts and amplitude ratios, between light curves obtained in di?erent ?lters, for modal discrimination of the main excited modes. Results. The detailed frequency analysis revealed a very rich and dense pulsational content consisting of 25 signi?cant peaks, 22 of them corresponding to independent modes: one is the already known main periodicity f0 = 25.5765 cd−1 (?V = 153 mmag) and the other 21 are excited modes showingverysmallamplitudes.Someadditionalperiodicitiesareprobablystillremainingintheresiduals.Thisrepresentsthemostcomplex spectrum ever detected in a high-amplitude pulsator of this type. The majority of the secondary modes suspected from earlier works are con?rmed here and, additionally, a large number of new peaks are detected. The amplitude of the main periodicity f0 seems to be stable during decades, but the majority of the secondary modes show strong amplitude changes from one epoch to another. The suspected fundamental radial nature of the main periodicity of BL Cam is con?rmed, while the secondary peak f1 = 25.2523 cd−1 is identi?ed as a nonradial mixed mode g4 with = 1. The radial double-mode nature, claimed by some authors for the main two frequencies of BL Cam, is not con?rmed. Nevertheless, the frequency f6 = 32.6464 cd−1 could correspond to the ?rst radial overtone.