Greater initial severity on the 30-item Positive and Negative Syndrome Scale (PANSS-30) correlates positively with antipsychotic-placebo separation and trial dropout, but it is unknown whether these associations are present also on PANSS-derived subscales. We assessed the relationship between initial severity and antipsychotic-placebo separation as measured by PANSS-30 and four PANSS symptom subscales: the positive (PANSS-POS), negative (PANSS-NEG), general (PANSS-GEN) and 6-item (PANSS-6) subscales, using patient-level data from 18 placebo-controlled risperidone and paliperidone trials. Analysis of covariance in the intention-to-treat population (last-observation-carried-forward) was used to assess antipsychotic-placebo separation and trial dropout. Across 6685 participants (90% schizophrenia, 10% schizoaffective disorder), the initial severity-by-treatment interaction was statistically significant for PANSS-30 (beta: −0.155;p< 0.001) and all PANSS subscales (beta range: −0.097 to −0.135;p-value range: < 0.001 to 0.002). In all cases, antipsychotic-placebo differences increased with initial severity. Judging by the distribution of relative outcomes (percent remaining symptoms), the interaction was partly explained by an increased chance of responding, but also by larger numerical responses in those who did respond, as initial severity increased. Except for PANSS-NEG, high initial severity on all PANSS scales predicted increased trial dropout, although not statistically significantly so for PANSS-6. In summary, we thus replicate previous findings showing greater initial severity to predict larger antipsychotic-placebo separation and extend these results to four PANSS subscales. For PANSS-POS and PANSS-GEN, but not for PANSS-NEG and PANSS-6, we also replicate the association between initial severity and trial dropout. Patients with low initial negative symptom severity were identified as a group of particular interest for further study since their results diverged most from the average both with regard to antipsychotic-placebo separation (low separation measured by PANSS-NEG) and trial dropout (high level).