Psoriasis is a chronic immune-inflammatory skin disease. Cross-sectional research examining diet quality indices (DQIs) in psoriasis has focused on the Mediterranean diet and is confined to Mediterranean populations, thereby lacking generalisability to other populations. We explored associations between DQIs and the likelihood of reporting a higher psoriasis severity. This was an online cross-sectional study recruiting adult volunteers with psoriasis (n=257). A 147-item food frequency questionnaire evaluated adherence to the Mediterranean Diet Score (MDS), the Dietary Approaches to Stop Hypertension (DASH) score, and the Plant-based Diet Index (PDI); original (oPDI), healthy (hPDI), and unhealthy (uPDI) subtypes. Psoriasis severity was determined with the self-assessed Simplified Psoriasis Index. When adjusted for age, sex, smoking, alcohol over-consumption, energy intake, and psychological morbidity, multinomial logistic regression analyses revealed an increased likelihood of reporting a higher psoriasis severity in participants with a very low adherence to DASH OR = 3.75, 95% CI 1.313 – 10.700, P = 0.01), and hPDI (OR = 4.04, 95% CI 1.251 – 13.064, P = 0.02) patterns. A reduced likelihood of reporting a higher psoriasis severity was shown in participants with low adherence to the uPDI (OR = 0.25, 95% CI 0.085 – 0.716, P = 0.01). With further adjustment for body mass index (BMI), a very low adherence to the oPDI was significantly associated with an increased likelihood of reporting a higher psoriasis severity (OR = 3.46, 95% CI 1.029 – 11.656, P = 0.05). Dietary interventions and assessment should be introduced in the care-pathway for psoriasis management.