Atopic dermatitis (AD) and psoriasis (PsO) are among the most common diseases in the daily clinical practice. Usually, AD and PsO are reported as two diseases that cannot coexist in the same patient because this requires the activation of opposing inflammatory pathways. Anyway, some reports highlight how AD and PsO may coexist in the same patient or develop consequently. In this short report we collected 12 patients that developed new AD or PsO. Among them, eight patients (n = 8; 3M:5F) with a previous diagnosis of PsO, developed subsequently an AD with a mean time of onset of 71.5 months. Out of eight patients, four patients where in treatment with ustekinumab, one with ixekizumab, two with adalimumab, and one with guselkumab. All new onset AD have been treated with topical medicaments, except one case that performed dupilumab. Contrariwise, four patients with a baseline AD developed a PsO with a mean time of onset of 25?months. Two AD patients were under dupilumab treatment, while the other two patients performed only topical treatments. All patients showed an improvement of the new onset PsO with topical treatment only. This report highlights how AD and PsO are not mutually exclusive diseases. The mechanisms by which AD patients develop PsO or psoriatic patients develop AD are still not very clear; some triggers can promote these processes, such as systemic therapies. Therefore, clinicians should carefully evaluate any changes in these patients, in order to reach a correct diagnosis and carry out a relative treatment.