Nowadays, the scientific community widely accepts the statement that silicon-substituted calcium phosphates have better biological properties compared to pure calcium phosphates. For example, a review published in this journal in 2007 started with the sentence "Silicon (Si) substitution in the crystal structures of calcium phosphate (CaP) ceramics such as hydroxyapatite (HA) and tricalcium phosphate (TCP) generates materials with superior biological performance to stoichiometric counterparts"[1]. A critical look at published articles demonstrates that this sentence is controversial and somehow misleading, because there is no experimental evidence that Si ions are released from Si-substituted calcium phosphates at therapeutic concentrations, and because there is no study linking the improved biological performance of Si-substituted calcium phosphates to Si release. The aim of this article is to explain this statement in more details.