  We find that the fluctuations of the condensate in a weakly interacting Bose
gas confined in a box of volume $V$ follow the law $<\delta N_0^2>\sim
V^{4/3}$. This anomalous behaviour arises from the occurrence of infrared
divergencies due to phonon excitations and holds also for strongly correlated
Bose superfluids. The analysis is extended to an interacting Bose gas confined
in a harmonic trap where the fluctuations are found to exhibit a similar
anomaly.
