  The smallest classically stable Q-balls are, in fact, generically metastable:
in quantum theory they decay into free particles via collective tunneling. We
derive general semiclassical method to calculate the rate of this process in
the entire kinematical region of Q-ball metastability. Our method uses
Euclidean field-theoretical solutions resembling the Coleman's bounce and
fluctuations around them. As an application of the method, we numerically
compute the decay rate to the leading semiclassical order in a particular
one-field model. We shortly discuss cosmological implications of metastable
Q-balls.
