Abstract Objectives: Determine the frequency of dermatological diagnoses in preterm newborns up to 28 days of life and associated perinatal factors. Method: a cross-sectional analytical study with a convenience sample and prospective data collection, was conducted between November 2017 and August 2019. Overall, 341 preterm newborns who had been admitted to a University hospital – including those admitted to the Neonatal Intensive Care Unit – were evaluated. Results: 61 (17.9%) had less than 32 weeks gestational age (GA), with a mean GA and birth weight of 33.9 ± 2.8 weeks and 2107.8 ± 679.8g (465 to 4230g), respectively. The median age at the time of evaluation was 2.9 days (4 h to 27 days). The frequency of dermatological diagnoses was 100% and 98.5% of the sample had two or more, with an average of 4.67 +1.53 dermatoses for each newborn. The 10 most frequent diagnoses were lanugo (85.9%), salmon patch (72.4%), sebaceous hyperplasia (68.6%), physiological desquamation (54.8%), dermal melanocytosis (38.7%), Epstein pearls (37.2%), milia (32.2%), traumatic skin lesions (24%), toxic erythema (16.7%), and contact dermatitis (5%). Those with GA< 28 weeks showed more traumatic injuries and abrasions, whereas those with ≥ 28 weeks had physiological changes more frequently, and those with GA between 34-366/7 weeks, had transient changes. Conclusion: Dermatological diagnoses were frequent in our sample and those with higher GA showed a higher frequency of physiological (lanugo and salmon patch) and transient changes (toxic erythema and miliaria). Traumatic lesions and contact dermatitis were among the 10 most frequent injuries, reinforcing the need to effectively implement neonatal skin care protocols, especially in preterm.