The marine ecosystem that has contributed to the discovery of cytarabine and its fluorinated derivative gemcitabine is now considered the most productive toll to acquire new natural derived anticancer entities. Few marine anticancer agents have entered clinical development, including bryostatin-1, dolastatin 10, LU103793, ET-743, kahalalide F, didemnin B and aplidine. The marine plitidepsin aplidine derived from the mediterranean tunicate Aplidium albicans is a synthetically produced anticancer agent that is structurally related to didemnins. Aplidines mechanism of action involves several pathways, including cell cycle arrest, inhibition of protein synthesis and antiangiogenic activity. Phase I studies have been reported for a number of several schedules including 1-hour, 3-hour and 24-hour infusion. Evidences of antitumor activity and clinical benefit of aplidine in several tumor types were noted across phase I trials, particularly in advanced medullar thyroid carcinoma. Phase II studies are underway. Within the entire phase I program, dose-limiting toxicities of aplidine were neuromuscular toxicity, asthenia, skin toxicity, and diarrhea. Interestingly, no hematological toxicity was observed. Aplidine displayed a very peculiar delayed neuromuscular toxicity that was found to be closely related to the symptoms described in the adult form of carnitine palmitoyl transferase deficiency type 2, which is a genetic disease treated with L-carnitine. Consistently, concomitant administration of L-carnitine allowed to improve aplidine-induce neuromuscular toxicity. In summary, aplidine is a novel marine anticancer agent with a very particular delayed neuromuscular toxicity that requires careful follow- up with promising antitumor activity.