Relatively little is known about the clinical course of symptoms in patients with a substance-induced psychosis (SIP) compared with those with a primary psychotic disorder (PPD). In this study, symptoms associated with psychosis were monitored across admission in two groups of patients: those with SIP (amphetamines or cannabis; n = 47) and those with PPD (n = 51). Sixty-two percent of patients were first admissions, 23% had one previous admission, and a further 14% had had two previous admissions. Symptoms were monitored using the Brief Psychiatric Rating Scale. Scores on the positive symptoms scale, negative symptoms scale, manic excitement, and negative mood were reported as was the extent of observed disturbed behavior at admission and then at Days 4/5, 8/9, 15/16, 22/23, 29/30, 36/37, 43/44, and 50/51. Patients with a SIP experienced more severe mania and disturbed behavior at admission than those with a PPD. However, these symptoms abated more rapidly for the SIP group during admission. Although positive symptom scores were equally high at admission for both groups, there was a more rapid abatement of these symptoms in the SIP group. Finally, negative symptoms were lower in the SIP group at admission and at Days 50/51, although the decline in symptoms was comparable in both groups.