Apremilast is an oral phosphodiesterase IV inhibitor recently registered for the treatment of psoriasis and psoriatic arthritis in Switzerland and other countries. Even though it offers only moderate efficacy compared to biologics, many patients prefer drugs given by the oral route. Apremilast is frequently used in private practice, as it showed no relevant safety signals in clinical trials and often, laboratory tests are omitted completely. Here we report a patient who developed acute lymphopenia and worsening of psoriasis during apremilast treatment, which resolved with discontinuation of apremilast. We suggest that at least in prospective registries, that regular monitoring of laboratory surrogate markers should be performed on a long-term basis to detect rare but potentially important safety signals.