In the past 10 years, the number of prisoners increased rapidly from 13,000 to 20,500 and the insufficient capacity of prisons became a serious problem. The study shows that the main reasons for the overcrowding of prisons are the immense increase of the probability that a detained offender is convicted together with the increase of the share of convicts receiving a prison sentence. These factors increased the number of prisoners by 3,300 and 3,100, respectively. Another less important reason for the growth of prison population is that the length of sentences has increased in the last two years. Furthermore, the prisoner numbers are affected by the declining crime rate. If crime did not decline in the previous years, the prisons would have to accommodate nearly 24,000 inmates. The study concludes that the current crime policy will lead to even further increase of prisoners. This is because of the dynamics of prisoners’ arrival and release. Due to recent tightening of crime policy, we have not yet reached a balance in the number of prisoners. The study suggests that a potential amnesty would bring only short-term relief and prisons would very quickly be filled again. At least a partial solution would be to use alternative penalties more frequently. If the crime policy continues on the same track, however, the capacity of prisons needs to be extended.