The results of a recent double-blind, randomized, placebo-controlled trial performed in 81 young patients at ultra-high risk for psychosis indicated that a 12-week intervention of 1.2g/day of ω-3 polyunsaturated fatty acids (PUFA) significantly reduced the risk of transition to psychosis and improved positive, negative and general symptoms as well as functioning. The aim of this post-hoc analysis was to determine at which time point ω-3 PUFAs start to significantly differ from placebo in improving psychopathology and functioning in young people at risk of developing psychosis. Analyses were performed using the mixed model repeated-measures analysis of variance. Compared to placebo, ω-3 PUFAs' significant effects on the amplitude of the reduction in General and Total PANSS scores are evident after the first four weeks of treatment; a reduction of positive symptoms and a lower mean PANSS positive score were apparent after eight weeks, whereas the significant drop in negative symptoms and the significant change and higher mean scores in global functioning occur later at 12weeks. The delay of onset of ω -3 PUFAs seems comparable to that of antipsychotics and antidepressants.