--- - |2+ Background There is limited information on the occurrence of ‘sudden gains’ – recognized improvements of substantial magnitude occurring between individual sessions of treatment. This study explores changes in anxiety across sessions of CBT for youth anxiety disorders to determine whether evidence exists for sudden gains in this population. Method A total of 133 anxious youth (Mage = 10.16 years; 55.6% male) were randomly assigned to receive 16 sessions of individual cognitive‐behavioral therapy (ICBT), family‐based CBT (FCBT), or a family‐based educational support and attention control (FESA). At each treatment session, youth completed a measure of anxiety. Sudden gains were calculated from weekly state anxiety scores using methods consistent with previous research (i.e., Tang & DeRubeis, 1999). Results Three participants experienced a sudden gain at any point during treatment; all experienced a reversal of the sudden gain, although one experienced a regain of the improvement that occurred during the sudden gain. Conclusions While sudden gains have been demonstrated in some studies, in a relatively new topic to the literature such as this, it should also be considered that many evidence‐based treatments are actually intended to produce more steady/gradual gains – which may be particularly true for youth who are not as cognitively advanced as adults and who have much to learn about how psychopathology – and for this analysis, anxiety – operates. - Journal of Child Psychology and Psychiatry, Page 251-257, October 2018.