Background Severity‐associated factors in atopic dermatitis (AD) have focussed on early onset, concomitant atopic diseases, markers of Th2‐shifted inflammation and filaggrin mutations. Objectives To investigate factors associated with severe AD in Finnish patients. Methods We conducted a single‐centre, cross‐sectional observational study with 502 AD patients aged 4.79 to 79.90 years (mean 32.08 years). Disease severity was assessed with the Rajka–Langeland severity score and EASI and associated clinical signs were evaluated. Data regarding onset, relatives, atopic and other comorbidities was gathered retrospectively. We investigated total serum IgE‐levels, a panel of filaggrin null mutations and functional variants of genes associated with skin barrier defects. Results Factors more frequent in severe AD included early onset (P = 0.004, 95%CI 0.000–0.024), male sex (P = 0.002, 95%CI 0.000–0.11), history of smoking (P = 0.012, 95%CI 0.000–0.024), concomitant asthma (P = 0.001, 95%CI 0.000–0.011), palmar hyperlinearity (P = 0.013, 95%CI 0.014–0.059), hand dermatitis (P = 0.020, 95%CI 0.000–0.029) and history of contact allergy (P = 0.042, 95%CI 0.037–0.096). Body mass indices (P < 0.000, 95%CI 0.000–0.011) and total serum IgE‐levels (P < 0.000, 95%CI 0.000–0.011) were higher in severe AD. No differences were observed for allergic rhinitis, allergic conjunctivitis, food allergy, peanut allergy, prick positivity, keratosis pilaris, history of herpes simplex infections, filaggrin null mutations and other gene variants. Conclusions Severity determinants in Finnish patients seem to be early‐onset, male sex, smoking, overweight, concomitant asthma, palmar hyperlinearity, hand dermatitis and high IgE‐levels. A sub‐typing of patients in relation to confirmed severity determinants may be useful for course prediction, prognosis and targeted AD management.