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Simple Summary: While previous studies showed that sperm quality has decreased over the last decades, others did not report such reductions, suggesting that the region where the population is evaluated has an influence. The current research, which was conducted on a regional scale, did not find variations in sperm count but did observe a drop in sperm motility and morphology. Semen quality has a direct relation to male fertility. Whether sperm variables in humans have decreased over the last years is still uncertain, with some studies showing a decline and others reporting no changes. In this regard, previous research has suggested that lifestyle and environmental conditions may contribute to this variability, calling for regional studies. The present work is a retrospective, unicentric study that includes semen samples analyzed between 1997 and 2017 at the Parc Taulí Hospital (Barcelona metropolitan area). First, a multivariate analysis including the age as a confounding factor showed a statistically significant decrease in semen volume, pH, progressive motility, morphology and total motile sperm over time. Contrarily, no significant variation in sperm count or concentration was observed. Mean reductions per year were −0.02 mL for volume, −0.57% for progressively motile sperm and −0.72% for sperm with normal morphology. Interestingly, the average annual temperature registered by the Spanish Meteorology Agency negatively correlated to sperm morphology and sperm count (Rs = −0.642; p = 0.002 and Rs = −0.435; p = 0.049, respectively). In conclusion, the present study based on infertile patients from the Barcelona area found a decline in sperm motility and morphology, without effects on sperm count. Changes in temperature appeared to be associated to this decline, but further studies are needed to address the mechanisms linked to the observed variations. [ABSTRACT FROM AUTHOR]